LIBRARY 

OF   THE 

UNIVERSITY  OF  CALIFORNIA. 

/ 

.V 

Class 


PYRITE 
SMELTING 


Edited  by 

T.  A.  RICKARD 


FIRST    THOUSAND 


NEW  YORK  AND  LONDON 

THE  ENGINEERING  AND  MINING  JOURNAL 
1905 


Copyright,  1905, 

By 
The  Engineering  and  Mining  Journal 


INDEX. 


Page. 

Preface    5 

Questions    6 

T.  A.  Rickard  (Introduction)..       7 
L.     S.    Austin 17 

E.  P.  iMathewsoa 21 

Walter  E.   Koch 23 

S.  E.  .Bretherton. 27 

F.  R.  Carpenter S3 

W.   R.   Ingalls 39 

R.  L.  Lloyd  45 

W.  T.  Keith  50 

Herbert  Lang 51 

L.  D.  Godshall 63 

William  A.  Hey  wood 78 

G.  F.   Beardsley 81 

Thomas  T.  Read 86 

Henry  W.  Edwards 91 

Charles  H.   Fulton 94 

P.  Wiseman 98 

W.   H.    Nutting 103 

W.  H.  Freeland 108 

William  A.  Heywood 118 

E.  A.  Weinberg 121 

Walter  E.   Koch 124 

W.   H.   Freeland 128 

Amado  Buen  130 


Page. 

Edward  D  Peters 132 

Hiram  W.    Hixon 193 

Walter  E.  Koch 195 

G.   F.   Beardsley 197 

9.    Dillon-Mills    203 

L.    S.    Austin 206 

Herbert  Lang 208 

Walter  E.   Koch 218 

G.    F.   Beardsley 219 

Lewis  T.  Wright 224 

Charles  S.   Palmer -. .  232 

Hiram  W.  Hixon 237 

S.    E.    Bretherton 243 

Lewis  T.   Wright 245 

P.    L.    Mareton 249 

J.  Parke  Channing 253 

W.    Randolph   Van  Liew 266 

J.  Parke  Channing 272 

William   A.    Heywood 276 

George   W.    Metcalfe 279 

James  W.  Neill 284 

E.   P.   Mathewson 237 

C.  H'.  Doolittle 292 

Smelting   at    Mt.    Lyell,    Tas- 
mania   .  . .  299 


PREFACE. 

This  volume  is  a  reprint  of  the  discussion  on  Pyrite 
Smelting  which  ran  through  various  issues  of  The  Engi- 
neering and  Mining  Journal  between  October,  1903,  and 
February,  1905.  The  contributions  have  been  revised 
by  the  respective  authors,  and  the  editorial  comment  ap- 
pearing at  intervals  in  the  Journal  has  been  modified  into 
the  introductory  remarks,  which  now  precede  the  suc- 
cession of  letters  contributed  by  no  less  than  twenty 
metallurgists.  Emphasis  was  placed  upon  the  value  of 
the  discussion,  and  a  notable  addition  was  given  to  the 
permanent  usefulness  of  it,  by  a  review  prepared  by  Dr. 
Edward  D.  Peters,  the  professor  of  metallurgy  at  Har- 
vard University. 

Earlier,  in  1903,  a  discussion  arose  consequent  upon 
an  article  dealing  with  the  relation  between  hearth-area 
and  furnace  capacity ;  this  article  and  the  criticism  which 
it  elicited  are  also  published  in  this  volume,  together 
with  three  other  papers  germane  to  the  subject. 


QUESTIONS. 

The  following  ten  questions  were  sent  out  by  the 
Editor  of  The  Engineering  and  Mining  Journal,  and 
formed  the  basis  for  the  ensuing  discussion : 

1.  What  types  of  ore  are  suited  to  the  process? 

2.  Is  hot  blast  advisable? 

3.  To  what  extent  can  fuel  be  eliminated? 

4.  What  amount  of  copper  is  required  for  the  collec- 
tion of  the  precious  metals  ? 

5.  What  percentage  of  lime  is  necessary  to  a    clean 
slag? 

6.  What  percentage  of  zinc  in  the   charge    can    be 
treated  profitably? 

7.  What  is  the  degree  of  desulphurization  attainable  ? 

8.  What  are  the  possibilities  as  to  capacity  of  furnace  ? 

9.  What  are  the  limitations  of  the  process? 

10.  What  is  the  relative  economy  as  compared  to 
rival  processes? 


INTRODUCTION. 

The  direct  smelting  of  sulphide  ores  is  a  branch  of 
modern  metallurgy,  the  importance  of  which  has  been 
enormously  increased  during  the  last  five  years.  As  an 
aid  to  the  beneficiation  of  low-grade  copper  ores,  carry- 
ing small  values  in  the  precious  metals,  this  method  of 
treatment  has  formed  the  basis  for  the  commercial  suc- 
cess of  several  big  mines  in  the  United  States,  British 
Columbia  and  Tasmania,  and  promises  to  play  a  much 
larger  part  in  the  future  development  of  other  regions. 

With  a  view  to  eliciting  the  best  professional  opinion 
upon  the  factors  controlling  the  success  of  this  type  of 
smelting,  we  sent  a  list  of  questions  to  a  number  of  suc- 
cessful metallurgists.  Their  replies  were  published  in 
the  discussion  department  of  The  Engineering  and  Min- 
ing Journal,  with  the  hope  that  those  of  our  readers  who 
possessed  experience  in  this  branch  of  technical  practice 
would  contribute  their  views  freely. 

This  hope  has  been  abundantly  fulfilled,  and  it  is  with 
much  gratification  that  I  am  now  enabled  to  republish, 
in  more  accessible  form,  the  practical  discussion  which 
grew  out  of  the  questions  put  to  my  professional 
friends. 

The  term  'raw  sulphide  smelting*  was  used  in  start- 
ing the  debate,  and  it  was  defined1  as  "the  treatment  of 
unroasted  sulphide  ores  with  a  view  to  the  formation  of 
matte."  It  was  held  that  'pyritic'  smelting  and  'matte* 
smelting,  as  metallurgical  terms,  failed  to  cover  the 
ground,  because  at  first  sight  the  former  seemed  to  omit 
pyrrhotite  ores,  themselves  an  integral  part  of  the  mate- 

iThe  Engineering  and  Mining  Journal,  October  10,  1903. 


INTRODUCTION. 

rial  to  be  considered  in  this  connection,  while  the  second 
included  the  treatment  of  pyrite  which  has  been  pre- 
viously roasted,  in  part  or  altogether.  But  objections, 
well  sustained,  were  made  to  the  use  of  'raw  sulphide' 
as  descriptive  of  the  reduction  of  pyritic  ores  "by  the 
utilization  of  the  combustible  qualities  of  the  sulphur 
and  iron  with  a  view  to  the  formation  of  matte."1  Mr. 
W.  R.  Ingalls  made  the  point  that  'matte'  smelting 
carried  with  it  a  reference  to  the  product  that  is  aimed 
at  by  the  process;  on  the  other  hand,  it  is  fair  to  say 
that  'pyritic'  smelting  suggests  the  kinds  of  ore  sus- 
ceptible of  treatment;  finally,  'raw  sulphide'  smelting 
describes  the  chemical  condition  of  the  material  when 
sent  to  the  furnace.  Therefore  it  amounts  to  this,  that 
the  subject  under  discussion  is  the  treatment  of  pyritic 
ores  as  raw  sulphides  with  a  view  to  the  formation  of  a 
matte.  To  this  may  be  added  the  corollary  that  matte 
is  produced  with  the  intent  not  only  of  extracting  the 
copper,  but  also,  and  this  is  fully  as  important,  of  col- 
lecting the  small  quantity  of  precious  metals  occurring 
in  the  ores. 

It  is  this  last  aspect  of  the  inquiry  that  Mr.  Godshall 
seeks  to  emphasize,  and  he  also  regards  'matte'  smelt- 
ing as  a  branch  of  'pyritic'  smelting ;  but  this  is  scarcely 
an  inference,  because,  as  we  have  said,  the  one  term 
refers  to  the  material  treated  and  the  other  to  the  prod- 
uct of  that  treatment;  so  they  rank  equally  in  descrip- 
tive value.  The  very  fact  that  matte  smelting  may  in- 
clude the  treatment  of  roasted  ores  does  not  make  it 
more  comprehensive,  but,  it  seems  to  us,  less  definitive. 
Roasted  ores  are  not  a  characteristic  charge  in  this  form 
of  smelting,  any  more  than  the  treatment  of  flue-dust 
is  characteristic  of  ordinary  blast-furnace  work;  it  is 
merely  incidental. 

'Sulphide'  smelting,  indeed,  may  seem  to  include  the 
treatment  of  any  sulphide,  and,  therefore,  for  example, 

*The  Engineering  and  Mining  Journal,  February  4,  1904. 


T.  A.  RICKARD. 

the  reverberatory  smelting  of  galena  or  the  reduction 
of  cinnabar ;  'matte'  smelting  fails  to  define  the  kind  of 
smelting  under  discussion,  because  it  also  covers  the 
production  of  copper  matte  in  reverberatory  practice. 

Tyritic'  smelting  describes  the  type  of  ore  treated; 
that  is,  the  iron  sulphides  which  have  a  combustible 
value.  It  includes  not  only  iron  pyrite,  but  also  the 
lower  sulphide,  pyrrhotite,  often  termed  magnetic 
pyrite;  it  includes  not  only  chalcopyrite,  but  arsenical 
iron  pyrite  as  well.  Thus  it  covers  the  ores  which  are 
essential  for,  and  particularly  adapted  to,  this  kind  of 
smelting — an  oxidizing  fusion  in  a  shaft-furnace.  But 
'pyritic'  is  wrong;  we  do  not  speak  of  a  'leady'  or  a 
'zinky'  smelting  when  describing  the  reduction  of  lead 
and  zinc  ores.  The  termination  *ic'  should  refer  to  the 
nature  of  the  process,  and  that  is  not  'pyritic,'  but  mat- 
ting— the  conversion  of  ore  into  matte. 

'Pyrite'  smelting  may  be  objected  to  as  covering  only 
common  pyrite,  that  is,  iron  sulphide,  whereas  the  pro- 
cess covers  the  treatment  of  all  the  pyrites,  not  only  the 
common  iron  sulphides — pyrite  and  pyrrhotite — but 
also  the  related  varieties  characterized  by  copper  and  by 
arsenic.  However,  the  employment  of  the  singular  to 
designate  the  type  which  it  represents  is  a  usage  neither 
infrequent  nor  incorrect.  Therefore,  we  finally  arrive 
at  the  conclusion  that  the  oxidizing  smelting  of  pyrite 
ores  in  a  shaft-furnace  with  a  view  to  producing  a  matte 
is  best  labeled  'pyrite  smelting.'  I  have  adopted  this 
term. 

The  practice  of  pyrite  smelting  is  based  upon  the 
utilization  of  the  heat  derived  from  the  combustion  of 
sulphide  ores  in  a  blast  furnace,  in  contradistinction  to 
the  heat  obtained  directly  from  carbonaceous  fuel.  Of 
the  sulphides,  those  of  iron  and  copper  are  the  best 
available,  the  sulphides  of  lead  and  antimony,  for  in- 
stance, being  prejudicial  to  successful  work  by  reason  of 
their  easy  volatilization  at  the  high  temperatures  re- 
ft 


INTRODUCTION. 

quired  for  a  proper  matte-fall,  while  the  sulphide  of  zinc 
tends  to  form  an  infusible  slag.  The  formation  of  matte 
and  its  downward  passage  through  the  charge,  play  the 
important  part  of  collecting  the  precious  metals  which 
may  be  disseminated  through  the  ores,  and,  in  this  way, 
render  the  process  a  form  of  concentration  by  fire  as 
contrasted  with  ordinary  wet  milling  practice.  This 
feature  of  the  process — the  formation  of  a  matte  which 
acts  as  a  collector  of  minute  quantities  of  precious 
metals — has  led  to  its  extended  application  during  re- 
cent years  in  the  treatment  of  pyrite  and  pyrrhotite  ores 
containing  small  quantities  of  gold  and  silver.  Copper 
sulphide  is  usually  considered  a  better  collector  than 
iron  sulphide  alone;  but  experience  has  proved  that  a 
very  small  percentage  of  copper,  in  the  presence  of  an 
iron  matte,  is  sufficient  to  yield  a  clean  slag.  What  the 
irreducible  minimum  of  copper  is,  remains  still  a  mat- 
ter for  difference  of  opinion,  and,  we  may  add,  a  sub- 
ject for  discussion  among  specialists. 

Just  as  in  the  concentration  of  ores  by  water,  it  is 
necessary  to  limit  the  number  of  operations,  because, 
aside  from  the  cost,  there  is  also  a  loss  entailed  bv  each 
treatment ;  so  in  raw  smelting  it  is  economical  to  con- 
centrate the  valuable  metals  in  as  few  smeltings  as  pos- 
sible. Ores  so  heavy  in  copper  and  iron  sulphides  as  to 
approximate  the  composition  of  matte,  itself  an  artificial 
sulphide,  do  not  gain  by  direct  smelting  unless  they  are 
mixed  with  silicious  material,  not  as  a  flux  alone,  but 
as  ore,  able  to  defray  a  portion  of  the  total  cost  of  treat- 
ment. When  one  operation  yields  a  40  to  50  per  cent 
matte  with  a  concentration  of  less  than  two  into  one,  it 
is  obvious  that  the  gain  secured  by  the  concentration 
may  be  largely  offset  by  the  cost  and  loss  in  treatment, 
so  that  it  may  be  more  profitable  to  dispose  of  the  ore 
otherwise,  as,  for  example,  by  reducing  its  sulphur  con- 
tent by  roasting  or  by  slagging  off  the  excess  of  iron 
by  a  preliminary  fusion,  so  that  it  may  become  part  of  a 

10 


T.  A.  R1CKARD. 

charge  containing  roasted  material  and  silicious  ores 
such  as  have  not  an  excess  of  iron  and  sulphur,  the 
matte-forming  ingredients.  When  the  ores  to  be  treated 
are  so  poor  in  copper  sulphides  as  to  form  a  low-grade 
matte,  requiring  further  concentration,  it  may  be  neces- 
sary, in  order  to  secure  a  high-grade  product  fit  for 
shipment,  to  repeat  the  process  so  many  times  as  to  en- 
tail a  cost  and  a  loss  in  treatment  which  will  not  justify 
the  result.  A  large  percentage  of  matte  usually  favors 
a  clean  slag  and  a  small  loss  in  precious  metals,  while  a 
small  proportion  of  matte  indicates  conditions  unfavor- 
able to  the  gathering  together  of  the  gold  and  silver, 
producing  an  unclean  slag. 

Nowadays,  near  well-established  mining  centers,  the 
problem  of  metallurgical  treatment  is  often  overcome 
by  the  disposal  of  ore  in  the  open  market ;  but  in  the 
early  days  of  a  new  mining  region,  before  custom 
smelters  offer  a  satisfactory  market  for  the  product  of 
the  mine,  it  is  frequently  economical  to  concentrate  the 
metals  into  a  high-grade  matte,  so  rich  that  the  expense 
of  transport  per  ton  of  original  crude  ore  is  compara- 
tively small.  The  shipment  of  bullion  from  a  stamp- 
mill  is  the  extreme  phase  of  the  same  view  of  the  prob- 
lem of  concentrating  the  values  into  as  small  a  bulk  as 
possible,  in  order  to  minimize  the  cost  of  transport  to 
the  refinery.  For  this  reason  small  matte-smelters  have 
flourished,  in  days  now  nearly  past,  in  the  mountainous 
parts  of  Colorado  and  in  the  deserts  of  Arizona — to 
mention  two  representative  conditions.  From  this  point 
of  view,  the  matte-smelter  may  be  regarded  as  a  metal- 
lurgical pioneer,  for  it  has  helped  notably  in  the  early 
development  of  mining  districts.  With  the  advent  of 
the  railway  and  the  consequent  nearness  to  industrial 
centers,  either  the  matte-smelter  has  been  shut  down  in 
the  face  of  the  facilities  afforded  by  central  establish- 
ments which  have  brought  the  ores ;  or,  when  the  mines 
of  any  one  locality  have  warranted  it,  the  matte-furnaces 

11 


INTRODUCTION. 

have  been  followed  bv  the  converter,  so  that  shipments 
of  matte  have  given  place  to  shipments  of  blister  copper. 

This  phase  of  the  subject  is  now  of  less  importance 
in  the  United  States,  although  in  the  more  remote  places 
of  the  earth  it  may  still  be  an  important  feature  in  the 
progress  of  mining.  At  the  present  time  pyrite  smelt- 
ing, in  this  country,  in  Canada  and  in  Mexico,  is  of  par- 
ticular importance  as  affording  a  cheap  method  of  bene- 
ficiating  those  pyrrhotite  and  pyrite  ores  that  carry 
small  quantities  of  gold  and  silver,  with  enough  copper 
to  permit  of  a  good  matte-fall.  As  the  costs  of  the 
operation  are  reduced  until  they  approximate  the  ex- 
pense of  stamp-milling,  the  smelting  of  such  ores  ren- 
ders valuable  a  proportion  of  gold  and  silver  which  not 
many  years  ago  was  considered  negligible.  With  the 
attainment  of  so  low  a  cost  for  raw  smelting  as  90  cents 
per  ton,  the  operations  of  the  furnace  begin  to  compare 
in  point  of  economy  with  the  wet-concentration  mill  and 
the  stamp-mill,  itself  held  to  be  the  cheapest  form  of  ore 
reduction  invented  by  man. 

The  consumption  of  fuel  is  a  phase  of  the  subject  on 
which  light  was  badly  needed  j1  and,  when  the  discussion 
developed,  valuable  data  were  forthcoming,  as  the 
pages  of  this  little  volume  testify.  Is  it  obviously  neces- 
sary, in  order  to  achieve  maximum  economy,  to  calcu- 
late the  relative  consumption  of  carbon  when  adding 
fuel  to  the  charge  in  the  furnace,  consuming  carbon  in 
heating  the  blast,  or  consuming  carbon  when  increasing 
the  volume  and  raising  the  pressure  of  the  blast?  In 
other  words,  is  it  cheaper  to  expend  fuel  on  the  blast 
before  it  enters  the  furnace  or  to  employ  fuel  direct  in 
the  smelting  operation?  Obviously,  to  a  large  extent, 
this,  like  the  tariff,  will  be  a  local  question,  and  will  de- 
pend upon  the  cost  of  fuel  and  the  relative  amount  re- 
quired by  different  ores ;  but,  however  put,  this  is  the 
main  question  at  issue  between  the  metallurgists  who 

iThe  Engineering  and  Mining  Journal,  May  12,  1904. 

12 


T.  A.  RICKARD. 

employ  pyrite  smelting;  as  Mr.  Ing-alls  has  put  it: 
"What  is  the  cheapest  way  of  getting  rid  of  your  sul- 
phur?" 

In  this  connection  it  is  a  question  whether  the  ex- 
tremely small  proportion  of  carbonaceous  fuel  used  in 
pyrite  smelting  does  indeed  take  any  physical  part  in 
keeping  the  charge  open  to  the  passage  of  furnace 
gases;  on  the  other  hand,  it  is  certain  that  the  minute 
you  increase  the  percentage  of  coke  in  raw  smelting, 
you  are  apt  to  fuse  the  charge  too  quickly  and  pre- 
vent oxidation  of  the  iron,  the  result  being:  a  liability 
to  an  extremely  silicious  slag  or  else  a  silicious  skeleton 
in  the  furnace,  which  means  a  freeze-up. 

To  prevent  this  evil  effect  of  the  coke,  to  obtain  its 
mechanical  aid  in  keeping  crusts  off  the  jackets,  and  to 
prevent  the  too  sudden  fusion  of  the  sulphides,  it  has 
been  found  best  to  feed  the  coke  to  the  sides  of  the 
furnace.  This  is  the  Mt.  Lyell  practice,  also,  recently 
adopted  at  the  Tennessee  Copper  plant 

The  doubts  thrown  upon  the  value  of  heating  the  blast 
provoked  a  lively  controversy,  which  became  quieted 
by  the  impressive  effect  of  the  facts  brought  out  during 
the  progress  of  the  discussion.  This  important  prob- 
lem has  been  clarified.  Beside  the  testimony  given  by 
Mr.  Walter  E.  Koch  and  Mr.  S.  E.  Bretherton,  we  can 
state  that,  at  a  well-known  establishment  treating  raw 
nickel-copper  pyrrhotite,  under  varying  conditions  of 
charge,  with  roasted  and  raw  ore,  and  from  8  per  cent 
down  to  3  per  cent  coke,  it  was  found  that  the  grade  of 
the  matte  was  not  appreciably  higher  than  when  the  cold 
blast  was  used.  The  ores  contained  3  per  cent  copper 
and  3  per  cent  nickel,  and  a  concentration  only  of  from 
4.5  to  6  into  one  was  desired.  The  blast  temperature 
was  500°  C.  The  metallurgist  in  charge  came  to  the 
opinion  that  hot  blast  was  advisable,  but  that  direct 
smelting  was  extremely  hazardous  because  the  furnace 
"was  likely  to  quit  without  notice,"  in  other  words, 

18 


INTRODUCTION. 

freeze  up.  He  concluded  that  heap-roasting  and  rapid 
smelting  were  preferable  to  double  smelting  with  hot 
blast.  But  he  had  an  unusually  bad  ore  to  treat,  and 
his  experience  was  exceptional.  Processes  were  made 
after  ores  were  fashioned. 

During  the  progress  of  the  discussion  a  practical  and 
forcible  comment  upon  it  has  been  offered  by  the  deci- 
sion, after  proper  trials,  of  the  Tennessee  Copper  Com- 
pany to  discard  the  practice  of  heap-roasting  prelimi- 
nary to  smelting,  and  to  smelt  the  raw  ores.  Until 
lately  the  low  costs  achieved  by  Mr.  Randolph  Adams 
and  Mr.  W.  A.  Heywood  had  enabled  the  advocates  of 
preliminary  roasting  as  against  straight  pyrite  smelting 
to  quote  the  costs  at  Ducktown  against  those  at  Mt. 
Lyell,  because  Mr.  Heywood's  costs  were  $1.8296  per 
ton  less  than  those  of  Mr.  Sticht,  who  omitted  roasting 
and  employed  double  smelting  with  hot  blast.  But  this 
comparison  is  no  longer  effective. 

The  value  of  the  practical  details  given  by  our  con- 
tributors will  be  appreciated  by  the  reader,  but  two  in- 
cidents bearing  upon  this  aspect  of  the  discussion  are 
worth  mention.  At  one  of  the  largest  establishments 
using  the  process  of  pyrite  smelting,  the  capacity  of  the 
furnaces  decreased  to  an  alarming  degree,  and,  despite 
unusual  skill  possessed  by  the  metallurgist  in  charge, 
this  decrease  was  wholly  unaccountable.  Just  at  this 
time,  when  the  problem  had  become  of  serious  moment 
to  the  commercial  side  of  the  operations,  one  of  our  con- 
tributors published  an  article,  which  appears  in  this 
volume,  referring  to  the  fact  that  analyses  for  alumina 
often  fail  to  distinguish  between  the  alumina  which  is 
already  tied  up  to  silica  and  satisfied  in  that  direction, 
and  the  alumina  which  is  available  in  slag-making.  This 
hint  saved  the  situation,  for  the  decrease  in  capacity  at 
the  smelter  referred  to  was  due  wholly  to  the  increased 
proportion  of  a  schistose  rock  encasing  the  ores.  An- 
other episode  worthy  of  record  was  a  visit  by  the  editor 

14 


T.  A.  RICKARD. 

of  this  little  volume  to  a  large  copper  smelter  in  Michi- 
gan, where  he  was  introduced  to  the  superintendent,  who 
at  that  moment  was  watching  the  'dipping  of  a  charge/ 
but  who  found  time  to  pull  out  a  notebook  from  a  pocket 
in  his  working  clothes,  and  to  exhibit  the  fact  that  it 
was  full  of  the  data  contributed  in  the  course  of  the 
discussion  on  pyrite  smelting,  the  very  material  which 
the  reader  will  find  on  the  pages  that  follow. 

Other  discussions  on  this  subject  will  doubtless  arise, 
and  each  later  one  will  afford  knowledge  more  accurate 
than  its  predecessor,  until  finally  that  metallurgical  mil- 
lennium is  reached  where  theory  merges  perfectly  into 
practice  and  there  is  nothing  more  to  be  said.  How- 
ever, that  date  belongs  to  the  Greek  Kalends.  In  the 
meantime,  the  close  of  the  present  discussion  marks  a 
stage  of  progress  which  is  epitomized  by  the  experience 
of  the  technical  men  at  the  Tennessee  Copper  Company's 
smelter  as  expressed  by  their  administrative  chief,  Mr. 
Channing.  During  the  period  of  two  years  covered  by 
the  interchange  of  views  on  pyrite  smelting,  Mr.  Chan- 
ning and  his  associates  have  been  applying  the  ideas  dis- 
tilled from  this  discussion,  and  at  their  smelter  they  have 
endeavored  to  work  out  some  of  the  problems  incidental 
to  the  development  of  a  successful  metallurgical  enter- 
prise. It  speaks  well  not  for  them  only,  but  for  the  new 
spirit  which  has  come  over  the  profession,  that  informa- 
tion of  so  detailed  a  kind  should  be  given  for  publica- 
tion where  it  will  prove  of  most  direct  service  to  the  in- 
dustry. We  shall  be  much  surprised  if  the  generous 
spirit  thus  evinced  is  not  met  half-way  by  those  in  charge 
of  similar  metallurgical  enterprises,  who,  possessing 
data  valuable  to  the  officers  of  the  Tennessee  Copper 
Company,  will  give  with  equal  generosity  from  the 
store  of  their  experience  also. 

It  cannot  be  said  that  pyrite  smelting  has  yet  reached  its 
culmination ;  on  the  contrary,  it  is  obvious  that  many 
questions  remain  unanswered  and  that  the  best  men  are 

15 


INTRODUCTION. 

strong  in  the  belief  that  radical  development  is  probable  in 
the  near  future.  The  question  of  hot  versus  cold-blast 
has  been  well  ventilated,  the  part  played  by  the  coke  has 
been  ascertained,  the  influence  of  zinc  is  recognized,  and 
so  forth;  but  the  main  point — the  possibility  of  concen- 
tration, of  making  a  matte  of  high  percentage  from  low- 
grade  ore  in  one  operation,  eliminating  the  cost  and  the 
loss  involved  in  repetition  of  treatment — this  is  a  prob- 
lem upon  the  successful  solution  of  which  the  future  of 
this  branch  of  copper  metallurgy  mainly  depends. 

T.  A.  RICKARD, 
Editor  of  The  Engineering  and  Mining  Journal 

June  29,  1905. 


CONTRIBUTION  BY  L.  S.  AUSTIN. 

The  Editor : 

Sir — I  take  pleasure  in  answering  the  questions  you 
have  submitted. 

I.  What  types  of  ores  are  suited  to  the  process! 

Sulphide  ores  of  iron  and  copper  (pyrite,  chalcopy- 
rite,  etc.)  in  quantity  sufficient  to  give  the  necessary 
matte-fall.  Ores  containing  lead  or  zinc  are  not  desir- 
able, though  they  may  be  added  sparingly.  In  such 
cases  part  of  the  lead  and  the  zinc  is  volatilized,  the  re- 
mainder going  into  the  matte  and  slag.  Silicious  ores 
containing  the  precious  metals  can  also  be  added  to  the 
charge  in  quantity  sufficient  to  form,  with  the  iron  of 
the  sulphide  and  other  ore,  a  suitable  slag.  Any  oxi- 
dized ores  containing  iron  and  copper  can  also  be  run 
with  the  addition  of  limestone  in  quantity  sufficient  to 
form  a  fluxing  mixture. 

2.  Is  hot  blast  advisable! 

Hot  or  even  warm  blast  is  of  assistance  in  raw  smelt- 
ing, but  in  the  past,  where  a  hot  blast  has  been  used,  it 
has  been,  in  several  cases,  abandoned.  It  is  probable, 
however,  that  where  the  hot-blast  apparatus  can  be  care- 
fully installed  and  properly  looked  after,  it  would  be  of 
great  advantage  to  use  it,  especially  in  undertaking  to 
smelt  a  very  silicious  or  comparatively  infusible  charge. 
Such  is  the  practice  at  the  Mansfeld  works  in  Germany. 

3.  To  what  extent  can  fuel  be  eliminated! 

In  the  older  methods  of  matte  smelting  10  to  15  per 
cent  of  fuel  is  used.  In  smelting  with  an  abundance  of 
sulphide  ore,  the  amount  has  been  cut  to  6  per  cent,  and 
at  times  to  even  a  less  quantity.  With  a  rapid-running 
charge  the  quantity  of  fuel  may  be  less  than  where  a 
slower-running,  silicious  charge  is  being  put  through. 

17 


PYRITE  SMELTING. 

4.  What  amount  of  copper  is  needed  for  the  collection  of 
the  precious  metals  ? 

A  charge  containing  sulphide  ores,  but  quite  free  from 
copper,  will  not  give  a  clean  slag,  but  with  as  little  as 
0.5  per  cent  of  copper,  this  object  can  be  attained.  This 
is  especially  the  case  where  the  other  conditions  for 
making  a  clean  slag  are  present,  viz.,  a  charge  free  from 
zinc,  the  use  of  sufficient  fuel  and  the  formation  of  a  fus- 
ible slag,  as  well  as  a  maximum  difference  between  the 
specific  gravities  of  the  slag  and  matte. 

5.  What  percentage  of  lime  is  necessary  to  a  clean  slag? 

Limestone  is  added  to  the  charge  in  quantity  suffi- 
cient, with  the  iron  available,  to  form  a  fusible  slag.  It 
has  not  been  the  aim  to  use  it  as  a  cleaner ;  but,  where 
present,  it  has  been  thought  to  act  in  this  manner.  Slags 
containing  as  little  as  5  per  cent  CaO  have  proved  clean. 

6.  What  percentage  of  zinc  in  the  charge  can  be  treated 
profitably  ? 

Zinc  up  to  10  per  cent  of  the  charge  has  been  treated 
successfully.  As  blende  it  goes  into  solution  in  the  slag, 
and  in  oxidized  form,  as  contended  by  some  metallur- 
gists, it  still  exists  in  solution,  and  not  as  an  active  base. 
Certainly  the  slag  becomes  stiffer  as  the  percentage  of 
zinc  increases.  The  specific  gravity  of  the  slag  becomes 
higher  and  its  separation  from  the  matte  is  less  perfect. 
Some  of  the  zinc  also  goes  into  the  matte,  rendering  it 
lighter,  and  thus  increasing  the  difficulties  of  separation. 
By  increasing  the  proportion  of  silicious  ore  we  produce 
more  slag  to  dissolve  and  carry  off  the  zinc,  thus  pro- 
moting the  ease  of  separation  in  the  furnace.  In  pres- 
ence of  much  alumina,  zinc  acts  badly,  and  makes  con- 
tinual trouble,  so  that  such  combinations  are  to  be 
avoided. 

7.  What  is  the  degree  of  desulphurization  attainable? 

In  raw  sulphide  smelting,  where  pyrite  is  used,  its 
first  equivalent  of  sulphur  is  loosely  held,  and  is  largely 
driven  off  in  the  upper  part  of  the  furnace.  It  has  been 

18 


L.  5.  AUSTIN. 

found  in  practice  that  at  least  66  per  cent  (two-thirds) 
of  the  sulphur  is  driven  off,  or,  at  most,  only  34  per  cent 
is  left  to  enter  the  matte  and  slag.  The  metallurgist 
should,  as  soon  as  possible,  determine  the  quantity  of 
sulphur  both  in  his  matte  and  in  the  slag,  as  a  basis  of 
calculation  for  his  charges.  He  can  calculate  the  quan- 
tity of  slag  from  the  known  silica  contents  of  his  charge, 
and  he  must  keep  account  of  the  weight  of  the  matte- 
fall  as  compared  with  the  tonnage  put  through. 

8.  What  are  the  possibilities  as  to  capacity  of  furnace? 
The  speed  at  which  a  given  matting  furnace  can  be 

driven  depends,  other  things  being  equal,  upon  the  na- 
ture of  the  charge.  A  silicious  charge  drives  slowly. 
Zinc  and  alumina  also  cause  slow  running.  On  the  other 
hand  the  mono-sulphides,  as  pyrrhotite,  conduce  to 
rapid  running,  since  there  is  no  first  equivalent  of  sul- 
phur to  drive  off  at  the  surface  of  the  charge,  and  the 
sulphur  gives  off  its  heat  lower  down  in  the  furnace, 
where  it  is  most  useful.  Above  all,  a  fusible,  somewhat 
basic  slag,  produces  rapid  running.  An  open  charge, 
where  there  is  no  excess  of  fines,  is  also  an  advantage. 
Where  all  these  favorable  conditions  exist  together,  as 
in  the  Boundary  district  of  British  Columbia,  as  high  as 
450  tons  per  day  of  24  hours  have  been  put  through  a 
single  furnace. 

9.  What  are  the  limitations  of  the  process? 

Where  there  are  no  lead  ores,  matte  smelting  is  of- 
ten the  only  method  which  can  be  used  for  reducing 
ores.  Sometimes,  as  shown  at  Leadville,  it  can  be  used 
in  competition  with  lead  smelting.  In  this  case,  the 
omission  of  roasting,  the  rapidity  of  the  process,  the  low 
fuel  consumption,  all  assisted  in  giving  it  the  advantage. 
There  is  the  drawback  that  much  flue-dust  is  made ;  this 
should  be  bricked  before  it  is  re-smelted.  Practically, 
by  the  time  it  has  been  treated  over  again,  the  losses 
approach  the  percentage  loss  in  flue-dust.  In  other 
words,  to  collect,  brick  and  re-smelt  has  cost  nearly 

ID 


PYR1TE  SMELTING. 

what  the  flue-dust  contained.  As  before  intimated,  zinc 
and  alumina  are  detrimental  to  steady  running.  It  is 
the  uncertainty  o'  operation  which  tells  so  against  raw 
matte  smelting,  and  it  may  be  said  that  success  in  it  de- 
pends on  skill  in  furnacing.  Those  who  are  so  skilled 
keep  these  various  matters  almost  as  trade  secrets,  and 
indeed  the  operation  of  a  matte  furnace  requires  experi- 
ence, and  the  ability  to  judge,  from  the  appearance  of 
the  furnace,  what  remedies  to  apply  or  what  changes  to 
make.  The  writer,  for  example,  has  seen  where  merely 
changing  the  height  of  the  smelting  column  has  caused 
a  badly  operating  furnace  to  work  smoothly.  As  has 
already  been  indicated,  matte  smelting  depends  on  hav- 
ing a  supply  of  sulphide  ore  and  upon  there  being,  cop- 
per available  in  the  charge. 

L.  S.  AUSTIN. 
New  York,  Oct.  10,  1903. 


20 


CONTRIBUTION  BY  E.  P.  MATHEWSON. 

The  Editor: 

Sir — Herewith  please  find  replies  to  questions. 

1.  Types  of  ore  suited  to  the  process.    Any  ore  car- 
rying sulphur  in  the  form  of  iron  pyrite,  copper  pyrite 
or  pyrrhotite. 

2.  Hot  blast  is  advisable  where  it  is  necessary  to  in- 
crease the  grade  of  matte  produced,  provided  sulphur 
on  charge  is  not  excessive  and  where  coke  is  expensive 
and  coal  or  oil  cheap. 

3.  Fuel  can  be  eliminated  entirely,  provided  there  is 
sufficient  pyrite  in  the  ore  charged.    This  condition  is 
rarely  encountered,  the  lowest  practical  elimination  in 
the  United  States  being  probably  down  to  4  per  cent. 

4.  Copper  is  not  necessary  for  the  collection  of  the 
precious  metals ;  they  will  collect  readily  in  an  iron 
matte. 

5.  Lime  can  be  used  successfully  up  to  31  per  cent  of 
slag,  as  was  proved  at  Anaconda,  and  I  believe  higher 
percentages  have  been  used  elsewhere.    It  is  a  question 
of  relative  economy. 

6.  Zinc  has  not  been  found  in  large  quantities  in  the 
ores  of  this  vicinity,  so  that  the  limit  of  the  amount  that 
can  be  treated  profitably  has  not  been  reached  here. 

7.  The  degree  of  desulphurization  attainable  on  py- 
rite is  80  per  cent  with  the  Butte  ores ;  we  readily  get  75 
per  cent.     This  can  be  varied  with  the  depth  of  the 
charge  and  heat  of  blast. 

8.  Capacity  of  the  furnace  is  best  regulated  by  the 
means  of  getting  rid  of  the  slag,  and  the  facilities  for 
charging   the  furnaces.     We  consider  600    tons  in  24 
hours  the  capacity  of  our  56-in.  by  i8o-in.  at  the  tuyeres. 

21 


PYRITE  SMELTING. 

To  put  more  than  this  through  the  furnaces  would  re- 
quire another  crew  of  feeders,  which  would  not  be  econ- 
omy. 

9.  Limitations  of  the  process.    Ore  too  fine,  say  less 
than  quarter  mesh,  or  too  clayey.    To  have  good  work 
it  is  necessary  to  have  fairly  open  charge. 

The  percentage  of  sulphur  may  vary  greatly.  In  most 
cases  the  grade  of  matte  produced  fixes  the  limit  of  the 
process.  Where  the  matte  is  too  low  grade  by  the  raw 
smelting  process,  roasting  has  to  be  resorted  to.  The 
aim,  in  most  copper  smelters,  is  to  produce  50  per  cent 
at  the  first  smelting,  though  some  have  to  smelt  twice  to 
get  it  to  this  point,  roasting  the  first  matte  between  the 
smeltings.  Matte  charged  again  to  a  furnace  raw  loses 
hardly  any  sulphur  in  the  smelting  process,  as  it  merely 
smelts  and  runs  through  the  charge. 

10.  Relative  economy.     Where  this  process  can  be 
used  at  all,  it  is  practically  the  cheapest  known. 

E.  P.  MATHEWSON. 
Anaconda,  Montana. 


CONTRIBUTION  BY  WALTER  E.  KOCH. 

The  Editor : 

Sir — I  beg  to  inclose  answers  to  your  questions  on 
pyritic  smelting.  We  have  two  48-in.  water-jackets, 
with  twelve  3-5-in.  tuyeres.  The  distance  from  charging 
floor  to  tuyeres  is  57  in.  and  from  tuyeres  to  taphole 
1 8  in.  The  capacity  of  each  furnace  is  50  tons  per  24 
hours.  The  blast  is  heated  entirely  by  waste  gases  from 
the  furnaces  and  boilers  (and  gas-engines  later  on). 

The  analysis  of  our  slag  is : 

Silica 41  to  45  per  cent. 

Iron 27  to  31  (as  protoxide). 

Alumina 5  to     7,  seldom  above  5. 

Lime   5  to  15,  seldom  above  10. 

Magnesia 2  to     5  per  cent. 

The  color  is  green,  a  dark  green  silicate  of  protoxides. 

Pyritic  smelting,  so-called,  is  purely  a  roasting  pro- 
cess, and  what  we  cannot  burn  off  goes  to  matte,  so  that 
it  is  really  the  exact  opposite  of  ordinary  smelting. 

I.  What  types  of  ores  are  suited  to  the  process? 

All  kinds  of  ores  are  suitable  so  long  as  you  have 
sufficient  sulphur  and  iron.  We  find  after  two  years' 
continuous  practice  that  20  per  cent  of  FeS2  in  the 
charge  gives  good  results. 

We  have  three  well-marked  classes  of  ores : 

(1)  Quartz-pyrite  =  70  per  cent  quartz  and  30  per 
cent  pyrite. 

(2)  Spar  ores  =  35  per  cent  quartz,  10  per  cent  pyrite 
and  55  per  cent  calcite. 

(3)  Red  ores  =  40  per  cent  quartz,  25  per  cent  iron 
oxides,  20  per  cent  calcite  and  10  per  cent  alumina.  Also 
pure  pyrite  and  some  brown  iron  ores.    These  classes 
of  course  shade  off  into  one  another. 

A  general  analysis  of  the  ore  from  the  mine  made 
three  years  ago  gave :  Si,  44  per  cent ;  A12O3,  5  per  cent ; 

23 


PYR1TE  SMELTING. 

CaCO3,  32  per  cent;  MgCO3,  2  per  cent;  FeS2,  15  per 
cent ;  FeCO3,  3  per  cent ;  Cu,  0.25  per  cent ;  Mn,  0.20 
per  cent ;  Au,  0.5  oz. ;  Ag,  0.25  oz.  per  ton.  The  copper 
now  runs  about  one-half  of  one  per  cent  and  seems  to 
increase  with  depth.  We  have  also  more  iron  and  less 
lime  now.  This  sample  gave  poor  results,  both  with  bar- 
rel and  vat  chlorination,  and  cyaniding,  both  raw  and 
roasted ;  and  so  we  were  led  to  try  pyritic  smelting. 

2.  Is  hot  blast  advisable  ? 

A  warm  blast  of  200°  C.  is  a  sine  qua  non  with  us ;  it 
spelled  success,  cold  blast  meant  failure.  I  have  not  as 
yet  found  any  advantage  in  heating  above  200°  C.  Our 
hot  blast  costs  us  nothing  but  the  stove,  designed  at 
Pittsburg,  Pa.,  by  Mr.  John  Macdonald.  The  furnace 
itself  and  the  waste  heat  from  boilers  and  gas-engines 
will  give  all  the  heat  necessary  if  intelligently  applied. 
Furthermore,  with  a  hot  blast  you  can  run  clean  slags 
without  using  barren  fluxes  to  the  extent  required  in 
cold-blast  plants;  for  example,  lime  may  be  cut  down 
to  5  per  cent  without  danger. 

The  man  who  has  never  used  hot  blast  can  form  no 
opinion  on  its  use,  as  the  results  are  so  different  from 
cold-blast  practice.  It  not  only  saves  fuel,  but  gives  the 
smelter  a  wider  and  more  economical  range  of  clean 
fluid  slags,  and  makes  work  easier  and  pleasanter. 

3.  To  what  extent  can  fuel  be  eliminated  ? 

We  find  five  per  cent  of  coke  to  be  the  lowest  per- 
centage giving  good  results.  We  generally  use  7  per 
cent  of  the  ore  charged,  or  6  per  cent  of  total  charge. 

4.  What  amount  of  copper  is  needed  for  the  collection  of 
the  precious  metals  ? 

We  use  half  of  one  per  cent  of  copper  in  the  charge 
to  collect  the  gold  and  silver;  it  is  quite  sufficient  and 
the  slags  run  clean.  We  concentrate  fifteen  to  one,  *.  e., 
15  tons  of  ore  to  one  ton  of  matte ;  and  the  copper  runs 
from  7  to  8  per  cent  in  the  matte  which  we  ship  to  the 
smelter.  We  have  had  mattes  containing  only  one  per 

24 


WALTER  E.  KOCH. 

cent  of  copper  carrying  200  grams  of  gold  and  60  grams 
silver  with  a  perfectly  clean  slag. 

5.  W hat  percentage  of  lime  is  necessary  to  a  clean  slag? 
Seven  per  cent  of  lime  is  enough  with  hot  blast. 

6.  What  percentage  of  sine  in  the  charge  can  be  treated 
profitably  ? 

Zinc  sulphide  is  a  very  good  fuel,  but  I  do  not  know 
how  much  we  could  profitably  use. 

7.  What  is  the  degree  of  desulphurization  attainable? 
At  present  about  80  per  cent  of  the  sulphur  in  the 

charge  is  burned  off,  but  I  think  we  can  do  better. 

8.  What  are  the  possibilities  as  to  capacity  of  furnace? 
This  is  quite  unknown  to  us  at  present.  We  have  two 

48-in.  diam.  furnaces  running  continuously.  The  capac- 
ity is  50  tons  each  per  24  hours.  Our  new  furnace  is 
126  by  42  in.  and  7  ft.  high  frorn  base-plate  to  charging 
floor. 

9.  What  are  the  limitations  of  the  process  ? 

A  lack  of  sulphur  and  iron.    You  must  have  FeS,. 

10.  What  is  the  relative  economy  as  compared  to  rival 
processes ? 

In  our  case,  after  failing  with  freemilling,  concentra- 
tion, chlorination  and  cyanidation,  both  separately  and 
combined,  we  succeeded  in  saving  practically  all  our  val- 
ues by  pyritic  smelting.  To  me  it  seems  that  cyaniding  is 
the  only  possible  rival,  but  it  did  not  save  the  silver  and 
copper,  and  only  about  70  per  cent  of  the  gold  in  our 
case. 

We  take  the  ore  as  it  comes  from  the  mine  and  dump 
it  straight  into  the  furnace,  merely  spalling  the  big 
chunks.  The  ores  required  reducing,  in  rolls,  and  roast- 
ing for  both  chlorination  and  cyaniding  in  our  case,  and 
you  can  smelt  pyritically  about  as  cheaply  as  by  milling 
and  roasting.  A  milling  and  roasting  plant  costs  more 
than  a  pyritic  smelter  and  takes  more  power  to  drive  it, 
and  then  you  have  to  add  cost  of  cyanide  or  chlorination 
plant.  Again,  and  worst  of  all,  you  have  divided  super- 

25 


PYRITE  SMELTING. 

intendence,  the  millman,  roaster-man  (concentrator-man 
if  needed)  and  cyanide  expert,  all  have  to  be  considered ; 
whereas  by  taking  your  ore  straight  from  mine  to  fur- 
nace, this  friction  is  avoided.  The  copper  and  silver  lost 
in  the  cyanide  and  chlorination  methods  now  yield  us 
over  $100  per  day  and  the  sulphur  is  utilized  as  it  should 
be,  one  pound  of  sulphur  being  equal  to  half  a  pound  of 
coke  in  fuel  value.  As  far  as  I  know,  there  is  no  single 
process  which  can  save  practically  all  the  values  of  gold, 
silver  and  copper  in  ores  such  as  ours,  so  simply  and 
economically  as  the  hot  blast  pyritic  method. 

WALTER  E.  KOCH. 
Santa  Maria  del  Oro,  Mexico,  June  8,  1903. 


26 


CONTRIBUTION  BY  S.  E.  BRETHERTON. 

The  Editor : 

Sir — In  reply  to  your  ten  questions  in  regard  to  raw 
smelting,  "that  is,  the  smelting  of  sulphide  ores  without 
previous  roasting,"  I  shall  endeavor  to  answer  them  in 
the  order  in  which  they  are  given,  and  trust  my  replies 
will  be  as  interesting  to  the  readers  of  your  valuable 
paper  as  the  replies  of  others  to  the  same  questions  will 
be  to  me. 

i.  What  types  of  ores  are  suited  to  the  process? 

Types  of  ore  containing  gold,  silver,  copper  and  lead, 
if  the  value  of  the  lead  is  less  than  the  additional  cost  to 
roast  and  then  smelt  in  a  lead  furnace,  which  requires 
more  fuel  than  the  so-called  pyritic  process. 

We  put  all  ores  containing  less  than  10  per  cent  lead, 
unless  a  carbonate,  into  the  matting  furnace,  and  some- 
times ores  that  contain  more  than  10  per  cent  lead,  if 
they  are  refractory — that  is,  containing  a  high  percent- 
age of  zinc  and  arsenic. 

While  answering  No.  I,  I  deem  it  advisable  to  answer 
No.  9  at  the  same  time: 

9.  What  are  the  limitations  of  the  process  ? 

This  depends  a  great  deal  on  the  local  conditions. 
Where  a  company  is  running  a  custom  smelting  plant, 
and  can  dilute  the  zinciferous  ores  and  concentrates 
from  one  mine  with  the  clean  silicious  ores  from  another 
by  judicious  mixing,  zinc  ores  may  be  worked  off,  no 
matter  how  much  zinc  they  contain. 

Again,  if  base  ores  are  plentiful  and  contain  sufficient 
values  to  allow  what  is  usually  accepted  as  a  fair  treat- 
ment, the  smelter  may  treat  silicious  gold  and  silver  ores 
very  cheaply,  so  that  when  competing  with  small  mill- 

27 


PYRITE    SMELTING. 

ing  and  concentrating  plants,  where  the  cost  of  milling 
or  concentrating  is  at  least  $2  per  ton,  add  this  cost  of 
milling  to  the  cost  of  marketing-  the  concentrates,  wear 
and  tear  of  the  plant,  and  the  loss  in  the  slime  and  tail- 
ing (which  is  generally  15. to  40  per  cent  of  the  silver, 
from  10  to  25  per  cent  of  the  gold,  and  from  15  to  50 
per  cent  of  the  copper,  if  the  ore  contains  any  copper), 
and  it  will  come  to  an  amount  equal  to  the  cost  of  smelt- 
ing, that  is,  if  the  mine  is  conveniently  located  for  ship- 
ping to  a  local  smelter,  by  rail.  Of  course,  the  richer 
the  silicious  ores  are  in  precious  metals,  the  greater  the 
loss  in  dollars  and  cents,  and  the  easier  it  is  for  the 
smelter  to  compete  with  the  concentrating  or  milling 
plant. 

But,  in  the  San  Juan  region  of  Colorado,  in  Yavapai 
county,  Arizona,  and  other  sections  of  the  country,  the 
concentrating  mill  is  a  great  benefit  to  the  smelter, 
since  crude  ores  as  they  are  produced  from  the  mines, 
even  if  they  contain  values  to  stand  smelting  direct,  are 
often  too  silicious,  whereas  by  wet  concentration,  the 
mills,  by  their  treatment  of  the  lowest  grade  of  ores,  are 
not  only  putting  from  65  to  85  per  cent  of  the  values  of 
anywhere  from  two  to  fifteen  tons  of  low-grade  ores 
into  one  ton  of  concentrates,  i.  e.,  if  the  ore  is  at  all  suit- 
able for  concentration,  but  at  the  same  time  are  elimi- 
nating the  silica,  and  producing  a  basic  concentrate  to 
be  shipped  to  the  smelter,  which  it  in  turn  can  utilize  as 
a  base  to  flux  the  richer  but  still  silicious  ores  that  are 
shipped  from  the  mines  direct  without  concentration. 

2.  Is  hot  blast  advisable  ? 

To  this  question  I  must  emphatically  say  Yes,  for  the 
following  reasons : 

Increased  capacity  of  the  furnace.  (Of  course  the  in- 
creased tonnage  is  partly  offset  by  having  a  decreased 
amount  of  ore  to  smelt  by  preliminary  roasting,  on  ac- 
count of  the  loss  of  weight  in  roasting.) 

Saving  of  fuel  consumption  in  the  blast  furnace. 

28 


S.  E.  BRETHERTON. 

Saving  the  cost  of  preliminary  roasting,  and  the  sav- 
ing of  preparing  the  ore  for  roasting. 

Brighter  tuyeres,  and  less  trouble  in  keeping  them 
open. 

Less  trouble  with  ores  containing  zinc  fas  zinc  seems 
to  be  more  easily  desulphurized  in  the  blast  furnace  with 
forced  blast,  under  intense  heat,  than  it  is  in  the  ordinary 
calcining  furnace)  and  the  elimination  of  arsenic,  which, 
so  far,  has  not  been  successfully  accomplished  with  cold 
blast. 

The  advantages  in  the  use  of  hot  blast  just  enumer- 
ated, reduce  the  cost  of  smelting  nearly  half  on  the 
heavy  sulphide  ores,  and  make  success  possible,  when 
success  would  be  practically  impossible  with  ore  con- 
taining much  arsenic  and  zinc,  and  small  percentages  of 
lead  and  antimony,  which  are  so  heavily  penalized  by  the 
refineries  when  reduced  into  matte  with  cold  blast. 

3.  To  what  extent  can  fuel  be  eliminated  ? 

I  do  not  think  it  advisable  to  reduce  the  fuel  below 
4  per  cent  on  the  ore  and  flux,  although  it  is  possible  to 
run  for  days  at  a  time  as  low  as  3  per  cent  on  the  bur- 
den, that  is,  not  including  the  weight  of  the  fuel  itself. 

4.  What  amount  of  copper  is  needed  for  the  collection  of 
the  precious  metals  ? 

This  depends  somewhat  on  the  character  of  the  ore  to 
be  treated,  especially  where  there  is  much  zinc.  I  do 
not  think  it  advisable  to  smelt  with  less  than  I  per  cent 
copper  on  the  burden,  and  prefer  3.  per  cent.  Of  course, 
ores  averaging  as  low  as  one,  one-half  or  one-quarter 
per  cent  copper  can  be  smelted  by  re-smelting  a  small 
portion  of  the  matte  containing  the  accumulated  copper 
over  and  over  again  with  the  charge,  in  order  that  it  may 
continue  to  gather  the  values.  We  have  an  excellent  il- 
lustration here  of  the  advisability  of  using  sufficient  cop- 
per. Even  when  making  matte  as  high  as  15  to  25  oz. 
gold,  and  containing  from  300  to  400  oz.  silver,  with 
plenty  of  copper,  by  using  the  enriched  matte  over  and 

29 


PYR1TE  SMELTING. 

over  again  in  order  to  concentrate  the  copper  up  to  the 
shipping  point,  our  slags  are  as  low  in  gold  and  silver 
contents  as  when  making  a  matte  containing  only  4  or 
5  oz.  gold  and  100  oz.  silver  with  15  Ib.  and  less  copper 
on  the  1,500  Ib.  charge  burden,  the  slag  running  from 
trace  to  .03  oz.  gold  and  from  .25  to  i  oz.  silver  to  the 
ton. 

5.  What  percentage  of  lime  is  necessary  to  a  clean  slag? 

This  depends  a  great  deal  upon  the  amount  of  alu- 
mina and  magnesia  contained  in  the  ore  to  be  smelted, 
as  it  is  necessary  to  have  a  fluid  slag  of  light  specific 
gravity,  to  avoid  mechanical  losses  in  the  slag,  yet  not 
so  light  that  the  fluidity  of  the  slag  is  sacrificed.  For 
these  reasons  I  like  a  little  alumina  and  magnesia  in  the 
ore,  especially  when  we  have  plenty  of  iron  and  do  not 
care  to  use  too  much  lime.  Of  course,  where  parties 
are  anxious  to  smelt  as  much  silica  as  possible  with  as 
little  flux  as  possible,  and  magnesium  lime  rock  is  avail- 
able, one  would  naturally  think  it  would  be  a  very  desir- 
able flux,  as  magnesia  has  nearly  twice  the  combining 
power  with  silica  that  iron  has,  and  nearly  half  as  much 
again  the  combining  power  of  lime,  that  is  for  a  bisili- 
cate  where  i  per  cent  CaO  is  equal  to  1.07  per  cent  SiO2, 
I  per  cent  MgO  would  be  equal  to  1.5  per  cent  SiO2 ;  but 
we  well  know  what  an  infusible  slag  we  would  get  from 
a  bisilicate  of  magnesia.  As  a  rule,  I  have  found  a  bi- 
silicate  slag,  classing  the  alumina  as  an  acid  containing 
anywhere  from  22  per  cent  to  30  per  cent  Fe,  that  is, 
28.3  per  cent  to  38.6  per  cent  FeO  respectively,  to  give 
excellent  results,  the  balance  being-  CaO,  ZnO,  etc. 

On  several  occasions  I  have  endeavored  to  make  a 
slag  high  in  silica  and  alumina,  in  order  to  force  the 
alumina  to  act  as  a  base,  and  found  that  some  of  the 
silica  would  soon  show  on  the  surface  of  the  slag-pots 
not  fused,  and  the  slag  would  scarcely  run.  At  other 
times  I  have  been  able  to  make  slags  extremely  low  in 
silica,  on  account  of  its  alumina  contents.  Classing  alu- 

80 


S.  E.  BRETHERTON. 

mina  as  an  acid,  I  have  successfully  made  slags  ex- 
tremely clean,  containing  over  20  per  cent  alumina. 

Of  course  we  cannot  compare  sulphide  smelting  in 
shallow  furnaces,  where  both  time  and  reducing  agents 
are  limited,  with  the  deep  iron  furnaces,  where  they  use 
so  much  fuel,  causing  a  strong  reducing  action  and  an 
intense  heat,  especially  with  hot  blast. 

I  do  not  think  it  advisable  to  attempt  to  make  a  slag 
containing  more  than  12  per  cent  zinc;  that  is,  15  per 
cent  ZnO,  and  the  FeO  must  be  reduced  in  proportion. 
So  that  for  practical  running  I  would  put  the  maximum 
amount  of  ZnO  at  n  per  cent,  and  the  minimum  amount 
of  CaO  at  10  per  cent,  assuming  that  there  are  no  mag- 
nesia or  alkaline  bases  present. 

Of  course,  in  matte  smelting  it  is  not  practical  or  nec- 
essary to  figure  out,  as  we  do  in  lead  smelting,  the  exact 
combining  power  of  the  lime,  magnesia,  iron  and  zinc 
contents  with  the  silica,  and  know  that  the  slag:  will  con- 
tain to  within  0.5  per  cent  of  the  silica,  iron  and  lime,  be- 
iore  putting  on  the  charge,  as  in  sulphide  smelting  we 
have  to  depend  on  the  feeding  and  proper  oxidation  of 
the  furnace  for  all  our  iron,  so  that  a  little  carelessness 
on  the  part  of  the  feeder,  or  an  increased  amount  of  fuel, 
will  produce  more  matte  and  decrease  the  iron  in  the 
slag. 

6.  What  percentage  of  zinc  in  the  charge  can  be  treated 
profitably  ? 

This  question  is  answered  in  my  reply  to  No.  5. 

7.  What  is  the  degree  of  de sulphur isation  attainable"? 
This  is  a  question  I  cannot  answer  definitely,  for  the 

reason  that  in  making  up  a  charge,  the  first  thing  to  be 
considered  is  to  use  sufficient  silica  to  combine  with  the 
bases,  by  adding  enough  lime  or  magnesia  to  make  the 
slag  of  the  proper  specific  gravity.  My  experience  has 
been  that  by  the  time  this  is  done  the  percentage  of  sul- 
phur is  so  reduced  that  a  person  can  concentrate  any- 
where from  8  to  12  tons  of  ore  into  one  ton  of  matte, 

31 


PYRITE  SMELTING. 

• 

which  is  all  that  is  advisable,  and  have  a  proper  matte- 
fall  for  fast  running  and  keeping-  the  crucible  hot.  I  have 
made  much  higher  concentration  than  12  to  i,  but  found 
it  was  not  practicable  nor  successful,  and  for  this  reason 
I  cannot  answer  definitely  the  question  as  to  the  degree 
of  desulphurization  obtainable,  but  I  will  say  that  I 
think  a  concentration  of  12  tons  of  ore  into  one  ton  of 
matte  in  one  operation,  the  maximum. 

8.  What  are  the  possibilities  as  to  capacity  of  furnace? 
This,  as  in  cold  blast  smelting,  depends  a  great  deal 

upon  the  character  of  the  ore,  matte-fall  and  percentage 
of  copper  in  the  charge.  Plenty  of  copper  and  large 
matte-fall  means  faster  running  and  less  fuel  consump- 
tion than  a  limited  amount  of  copper  and  higher  con- 
centration, but  I  would  say  that  the  capacity  of  the  fur- 
nace with  hot  blast,  as  compared  with  cold,  would  be 
fully  one-third  more. 

9.  What  are  the  limitations  of  the  process? 
This  is  answered  in  the  reply  to  No.  I. 

10.  What  is  the  relative  economy  as  compared  to  rival 
processes  ? 

This  is  answered  in  the  reply  to  No.  2. 

S.  E.  BRETHERTQN. 
Val  Verde,  Arizona,  Oct.  10,  1903. 


32 


CONTRIBUTION  BY  F.  R.  CARPENTER. 

The  Editor : 

Sir — I  take  pleasure  in  answering  your  questions. 

1.  What  types  of  ores  are  suited  to  the  process? 

Any  gold,  silver  or  copper  ores  not  carrying  lead  in 
paying  quantities  may  be  treated  by  raw  smelting.  If 
the  ores  carry  no  sulphide  material,  as  at  Deadwood,  it 
must  be  added  in  quantities  at  least  sufficient  to  make  a 
matte.  If  they  carry  no  silica,  it  must  be  added  to  slag 
the  iron.  If  iron  is  scarce,  limestone  may  be  added  for 
flux.  If  sufficient  copper  is  in  the  charge  to  bind  the  sul- 
phur, satisfactory  slags  carrying  not  more  than  4  per 
cent  iron,  as  at  Mansfeld,  can  be  made.  If  jron  is  plen- 
tiful, lime  may  be  omitted. 

2.  Is  hot  blast  advisable  ? 

It  may  be  advisable,  but  I  am  sure  that  it  is  not  an 
absolute  necessity.  It  probably  lowers  the  zone  of  fus- 
ion to  a  point  nearer  the  tuyeres,  but  there  is  a  question 
as  to  the  desirability  of  having  it  there.  If  much  iron 
pyrite  is  to  be  oxidized,  the  'noses'  formed  in  front  of 
the  tuyeres  may  become  very  desirable  things  to  have ; 
in  any  case,  one  does  not  burn  much  iron  until  after  they 
are  formed.  If  the  hot-air  stoves  could  be  heated  by 
waste  gases,  as  in  iron  smelting,  it  would  pay.  It  re- 
duces the  fuel  to  the  extent  of  heat  so  added;  but  the 
best  hot-air  stove  made  is  a  very  wasteful  machine  when 
heated  with  extraneous  fuel,  as  a  large  percentage 
of  the  heat-value  of  the  fuel  is  lost.  I  have  never  found 
the  magic  in  mere  hot  air  that  others  have  professed  to 
find. 

83 


PYRITE  SMELTING. 

3.  To  what  extent  can  fuel  be  eliminated"? 

All  carbonaceous  fuel  can  be  eliminated,  and  in  ideal 
or  true  pyritic  smelting  it  is  highly  desirable  that  it 
should  be.  First,  the  process  is  an  oxidizing  process, 
and  not  reducing.  Second,  the  ignition  of  the  coke 
tends  to  fuse  the  unoxidized  pyrite,  causing  it  to  run 
away  in  the  form  of  low-grade  matte,  thus  losing  to  the 
charge  both  its  fuel  and  flux  values. 

4.  What  amount  of  copper  is  needed  for  the  collection  of 
the  precious  metals  ? 

It  depends  somewhat  upon  the  degree  of  concentra- 
tion attempted.  If  very  little  matte  is  made,  it  should 
carry  perhaps  10  per  cent  copper.  If  a  very  large  per- 
centage of  matte  is  made,  2  or  3  per  cent  of  copper  is 
sufficient.  This  would  mean  that  the  charge  should 
carry  only  traces  of  copper.  If  the  ores  carry  both  gold 
and  silver,  and  a  fair  quantity  of  matte  is  made,  copper 
may  be  entirely  avoided.  We  ran  the  Deadwood  plant 
for  four  years  without  other  than  mere  traces  of  copper 
in  the  matte,  certainly  less  than  one  per  cent.  The  slags 
carried  from  fifty  cents  to  one  dollar  and  a  half  in  gold, 
and  invariably  ran  up  and  down  in  proportion  to  the 
quantity  of  matte  made.  I  do  not  think  that  the  addi- 
tion of  copper  in  after  years  made  much  difference  in 
the  saving  of  the  silver,  but  it  did  help  in  the  saving  of 
the  gold.  I  ran  all  grades  of  copper  matte  from  mere 
traces  to  30  to  40  per  cent  copper.  Beyond  10  per  cent 
there  was  no  gain.  Our  matte  at  Golden  averages  6  per 
cent  copper. 

5.  What  percentage  of  lime  is  necessary  to  a  clean  slag? 

In  ideal  pyrite  smelting,  lime  is  a  nuisance  to  be 
avoided  if  possible.  It  costs  money  to  purchase  it,  labor 
to  handle  it,  fuel  to  smelt  it,  and  it  adds  to  the  quantity 
of  slag  made,  thereby  increasing  the  quantity  of  slag 
losses.  In  the  formation  of  the  slag  it  takes  the  place 
of  iron,  thereby  lessening  the  degree  of  concentration. 

84 


F.  R.  CARPENTER. 

Upon  the  other  hand,  it  tends  to  lessen  the  specific  grav- 
ity of  the  slag,  and,  within  limits,  lowers  its  fusing 
point.  I  have  not  succeeded  in  using  lime  to  an  ad- 
vantage where  I  sought  to  do  genuine  pyritic  smelting. 
I  think,  all  things  considered,  especially  if  the  ores  carry 
alumina,  lime  had  best  be  avoided,  particularly  in  the 
first  smelting.  The  following  slag  is  made  at  Golden 
with  a  cold  blast  and  5  per  cent  coke : 

Silica 33.50  per  cent. 

Iron 32.26    '.' 

Lime 11.42    " 

Alumina 12.00    " 

with  small  quantities  of  magnesia,  alkalies,  etc.,  to  bal- 
ance. It  is  practically  free  from  gold,  silver,  and  copper. 

6.  What  percentage  of  zinc  in  the  charge  can  be  treated 
profitably  ? 

I  do  not  know.  A  little  zinc  seems  to  make  no  trou- 
ble. It  goes  partly  into  the  matte,  partly  into  the  slag, 
and  partly  up  the  chimney.  The  smelter  at  Buena  Vista 
has  treated  ores  heavy  in  zinc  and  the  experience  ob- 
tained there  would  doubtless  prove  of  value  in  elucidat- 
ing this  branch  of  the  inquiry. 

7.  What  is  the  degree  of  de  sulphur  ization  attainable? 

It  depends  entirely  upon  the  charge.  With  pyrite, 
in  the  worst  cases  50  per  cent  of  the  sulphur  is  lost  at 
once  by  the  volatilization  of  one  atom  of  sulphur.  At 
Deadwood  in  former  days,  with  no  copper  and  but  little 
pyrite  in  the  charge,  we  often  failed  to  make  any  matte 
at  all,  the  whole  of  the  pyrite  being  oxidized  and 
slagged.  At  Golden,  Colo.,  and  at  Florence,  I  so  ar- 
ranged the  slag  elements  as  to  call  for  about  16  per 
cent  FeO.  In  a  lime-alumina-silica  slag,  such  as  I  make, 
the  furnace  can  be  depended  upon  to  take  this  amount 
of  iron  when  fed  in  the  form  of  pyrite.  There  is  a  select- 
ive action  in  the  furnace  upon  which  I  have  heretofore 
insisted ;  i.  e.,  with  a  given  ore  and  a  definite  amount  of 
limestone  the  slag  will  take  about  so  much  iron  and  no 

35 


PYRITE  SMELTING. 

more,  the  excess  remaining-  over  for  matte.  It  is  well  to 
study  the  requirements  of  the  furnace  and  supply  them. 
It  would  almost  seem  that  the  furnace  at  times  acted 
with  intelligence,  and  could  be  trusted  to  do  the  right 
thing1. 

8.  What  are  the  possibilities  as  to  capacity  of  furnace"? 
With  two  furnaces  of  the  same  size,  one  doing  pyritic 

smelting  proper  and  the  other  running  upon  ores  pre- 
pared by  roasting,  the  latter  will  smelt  twice  as  many 
tons  as  the  former ;  but  when  we  consider  the  time  lost 
in  roasting  the  ores  and  the  cost,  the  advantage  will  be 
found  with  the  first  furnace.  One  furnace  which  I  have 
used,  that  is  three  by  sixteen  feet  at  the  tuyeres,  running 
upon  a  charge  consisting  of  silicious  pyrite  and  lime- 
stone, and  making  the  following  slag,  with  either  hot  or 
cold  blast,  will  average  250  tons  of  charge  per  day : 

SiO2 38  to  40  per  cent. 

CaO 27  to  30    " 

FeO 16  to  18    " 

AlsOs 10  to  12    " 

If  this  furnace  were  50  per  cent  wider,  as  it  should  be, 
I  believe  it  would  smelt  50  per  cent  more  ore.  There  is 
no  iron  going  into  the  furnace  that  is  not  in  the  sul- 
phide form.  All  the  iron,  therefore,  in  the  slag  is  ob- 
tained from  the  burning  of  pyrite  within  the  furnace. 

9.  What  are  the  limitations  of  the  process"? 

As  I  understand  the  question,  there  are  practically  no 
limitations  if  the  ores  do  not  carry  lead.  In  smelting 
for  gold  and  silver,  if  the  ores  are  very  high  grade,  it 
would  probably  be  best  to  sell  them  to  lead  smelters. 
With  these  exceptions  I  think  the  question  is  answered 
in  my  reply  to  the  first  question. 

10.  What  is  the  relative  economy  as  compared  to  rival 
processes  ? 

The  roasting  of  sulphide  ores  is  avoided,  and  the  in- 
terest upon  the  large  amount  of  capital  tied  up  in  the 

36 


F.  R.  CARPENTER. 

roasting  heaps  saved.  In  the  actual  smelting,  fuel  is 
economized.  In  many  places  where  water  concentra- 
tion is  now  employed,  pyritic  or  raw  smelting,  by  rea- 
son of  its  closer  saving,  is  more  economical.  At  Dead- 
wood,  quantities  of  silica  were  slagged  off  and  ores 
treated  that  would  not  have  been  profitable  in  lead 
smelting. 

Without  meaning  to  criticise  smelting  as  now  carried 
on  at  Butte,  Mont.,  I  have  often  thought  that  raw 
smelting  along  the  lines  which  I  believe  I  was  first  to 
employ  at  Deadwood,  and  later  at  Golden,  would  be 
well  suited  for  Montana  orts,  and  would  result  in  the 
saving  of  much  of  the  concentrating  and  roasting  ma- 
chinery now  employed  there.  It  is  hardly  a  mere  opin- 
ion, as  I  have  smelted  many  thousands  of  tons  of  Butte 
ores. 

Let  us  suppose  that  by  mixing  the  more  silicious  with 
the  more  pyritiferous  ores  an  average  of  5  per  cent  cop- 
per, 55  per  cent  silica  and  alumina  could  be  maintained. 
I  do  not  know  the  cost  of  coke,  coal  and  limestone  at 
Butte,  but  upon  a  Denver  basis  the  cost  for  limestone, 
coke  and  hot  blast  sufficient  to  smelt  ores  of  the  above 
grade  would  be  $1.71  per  ton.  This  charge  is  now 
ready  for  smelting  raw,  and  to  it  must  be  added  the  cost 
for  administration,  labor,  etc.,  against  which  have  been 
saved  the  loss  by  concentration,  the  cost  of  concentra- 
tion and  the  cost  of  roasting.  There  are  slag  losses 
in  the  smelting  of  the  above  charge,  and  there  are  also 
slag  losses  in  the  present  method  of  smelting  calcines, 
but  the  above  lime-silica  slags  are  wonderfully  free 
from  copper,  gold  and  silver,  but,  of  course,  far  greater 
in  quantity.  I  cannot  say  that  the  total  amount  of  cop- 
per produced  would  upon  the  whole  be  greater,  but  I 
think  it  would.  The  resulting  matte  in  the  above  charge 
should  be  high  enough  for  immediate  bessemerizing; 
but  if  lower  grade  ores  were  used,  a  second  or  concen- 

37 


PYRITE  SMELTING. 

tration  smelting  might  become  necessary,  which  costs 
but  very  little  per  ton  of  original  ore. 

I  am  informed  that  the  loss  by  water  concentration  at 
Butte  is  19  per  cent.  If  it  is,  this  would  go  far  toward 
offsetting  the  extra  slag  loss,  if  any,  in  the  raw  smelting. 

F.  R.  CARPENTER. 
Denver,  Colo.,  Oct.  10,  1903. 


38 


CONTRIBUTION  BY  W.  R.  INGALLS. 
The  Editor : 

Sir — In  reply  to  your  request  to  participate  in  the  dis- 
cussion on  raw  sulphide  smelting,  allow  me  first  to  raise 
the  question  as  to  the  descriptive  phrase,  which  is  sub- 
stituted for  what  we  have  heretofore  known  as  'matte' 
smelting  or  'pyritic'  smelting.  Fault  can  be  found 
with  any  one  of  these  phrases,  yet  it  seems  to  me  that 
the  old  description  of  'matte'  smelting  is  least  open  to 
criticism.  It  refers  to  the  product  that  is  aimed  at, 
whether  the  crude  ore  be  smelted  raw,  or  roasted,  and, 
as  I  shall  attempt  to  show,  the  two  methods  merge  into 
each  other  so  that  there  is  no  sharp  dividing  line,  and  no 
one  misunderstands  what  is  meant.  On  the  other  hand, 
the  term  'raw  sulphide'  smelting  may  be  applied  to  other 
processes  than  the  smelting  of  a  pyritous  ore  to  a  matte. 
For  example,  galena  is  smelted  directly,  both  by  the 
precipitation  method  in  the  blast  furnace  and  by  the 
roast  reaction  method  in  reverberatory  furnaces  and 
Scotch  hearths,  and  those  certainlv  are  forms  of  raw  sul- 
phide smelting. 

In  the  matte  concentration  of  pyritous  ores,  every 
one,  who  has  attempted  a  roasting  in  heaps  or  stalls,  has 
observed  the  formation  of  stall  matte,  and  the  idea  of 
effecting  the  concentration  of  the  ore  bv  one  smelting 
operation,  utilizing  the  fuel  value  of  its  sulphur  contents, 
must  have  occurred  early  to  metallurgists.  This  was 
developed  into  the  process  of  pyritic  smelting,  which  ex- 
cited much  discussion  a  few  years  ago.  The  great  feat- 
ure of  that  process  was  to  dispense  entirely  with  the  use 
of  carbonaceous  fuel.  I  believe  that  has  indeed  been 

39 


PYRITE    SMELTING. 

done  at  Tilt  Cove,  Newfoundland,  and  at  Mt.  Lyell,  Tas- 
mania, but  in  general  it  has  not  proved  to  be  a  practic- 
able process.  The  smelting  of  raw  pyrite  with  a  com- 
paratively small  proportion  of  fuel  has  become,  how- 
ever, a  recognized  metallurgical  method,  which  is  em- 
ployed successfully  at  numerous  places.  The  distinction 
between  this  and  smelting  after  a  preliminary  roast  is 
only  one  of  degree,  and  the  choice  of  a  particular 
method  must  be  governed  in  each  case  by  the  condi- 
tions. 

In  most  blast  furnaces  employed  for  the  smelting  of 
cupriferous  pyrite  there  is,  beside  the  reducing  action, 
a  more  or  less  powerful  oxidizing  effect,  which  serves  to 
burn  off  part  of  the  sulphur  in  the  charge.  The  same  is 
true,  even  in  the  lead  blast  furnace,  and  it  is  now  the 
common  practice  to  put  rich  galenas  on  the  charge  raw, 
some  of  their  sulphur  going  into  the  matte  and  some  be- 
ing burned  off.  All  of  these  furnaces  have  a  factor  of 
oxidation,  which  must  be  known  approximately  before 
the  charge  can  be  calculated.  This  is  true,  whether  we 
are  considering  the  smelting  of  raw  pyrite  or  pyritous 
ore  that  has  previously  been  burned  down  to  7  or  8  per 
cent  sulphur.  The  chief  question  is,  What  is  the  cheap- 
est way  of  getting  rid  of  the  sulphur? 

In  this  connection  it  is  to  be  remarked  that  the  roast- 
ing of  pyritous  ores  is  not  necessarily  an  expensive 
process.  Lump  ore  can  be  roasted  in  stalls  for  about 
5oc.  per  ton,  including  transportation  to  the  furnace, 
and  the  first  cost  of  plant  is  moderate.  Fines  can  be 
roasted  with  the  lumps  to  the  extent  of,  say,  10  per  cent. 
Fine  ore  alone  is  roasted  at  Butte,  Mont.,  in  the  Mc- 
Dougal  type  of  furnace  for  as  low  as  33c.  per  ton,  not 
including  transportation  to  and  from  the  furnace.  In 
order  to  determine  the  best  method  of  smelting,  such 
figures  as  these  have  to  be  combined  with  the  cost  of  the 
blast-furnace  work,  taking  into  account  the  quantity  of 
fuel  consumed  in  the  latter,  the  rate  of  smelting,  the 

40 


WALTER  RENTON  INGALLS. 

matte-fall,  etc.  The  conditions  are  affected,  of  course, 
by  the  character  of  the  original  ore,  which  may  be  all 
fine,  or  composed  of  lumps  which  crumble  and  are  un- 
suitable for  stall  roasting.  In  large  operations  also,  the 
process  has  to  be  considered  in  connection  with  the  con- 
verting of  the  matte  into  blister  copper,  which  final  step 
is,  indeed,  pyritic  smelting. 

One  of  the  most  interesting  fields  of  matte  smelting 
is  the  concentration  of  values  at  mines  in  remote  loca- 
tions, as,  for  example,  in  Mexico.  Cases  can  be  found 
there  where  ore  worth  $50  per  ton  is  produced  at  local- 
ities whence  freight  and  treatment  charges  come  to  $70 
per  ton,  obviously  an  impossible  proposition,  without 
an  intermediate  step.  By  effecting  a  concentration  of  10 
to  i,  a  ton  of  matte,  worth,  say,  $400  to  $450,  may  be 
produced  from  10  tons  of  ore,  and  business  can  be  done. 
In  such  undertakings  small  furnaces  are  likely  to  be 
employed,  and  the  conditions  are  widely  different  from 
those  which  obtain  at  Salt  Lake  City,  in  British  Colum- 
bia and  other  places,  where  big  tonnage  is  to  be  han- 
dled ;  charcoal  may  be  the  only  available  fuel,  a  high  de- 
gree of  concentration  is  desirable,  and  comparatively 
easy-running  slags  are  likely  to  be  a  necessity.  I  am 
disposed  to  think  that  these  results  can  be  more  easily 
obtained  by  smelting  partially  roasted  ore  than  by  smelt- 
ing raw  ore. 

In  one  undertaking  of  that  kind,  we  aimed  to  burn  the 
ore  in  stalls  as  completely  as  possible.  There  was  a 
surplus  of  fines,  and  these  we  jigged,  putting  the  concen- 
trates on  the  stalls  as  covering.  The  furnace  was  a 
small  one,  and,  with  too  small  a  matte-fall,  gave  trouble. 
This  could  be  remedied  by  putting  on  the  charge  some 
raw  concentrates,  of  which  there  was  always  a  large  sup- 
ply, and  thereby  increasing  the  matte-fall.  If  there  is 
too  little  sulphur  in  a  charge  it  is  always  possible  to  tone 
it  up  to  any  desired  degree,  without  any  trouble  at  all. 

41 


PYRITE  SMELTING. 

We  had  an  ore  which  contained  about  50  oz.  silver  and 
I  oz.  gold  per  ton,  with  generally  about  i  per  cent  cop- 
per. There  was  a  high  recovery  of  gold  and  silver,  and, 
apparently,  there  need  be  no  fear  on  that  score,  when 
there  is  i  per  cent  copper  in  the  ore,  or  even  less.  An 
important  consideration,  however,  is  the  relative  spe- 
cific gravity  of  the  matte  and  slag,  and  the  temperature 
at  which  they  are  discharged  into,  and  maintained  in, 
the  settler.  The  loss  of  value  in  the  slag  is  due  largely 
to  particles  of  entrained  matte,  and  there  will  be  ob- 
viously the  best  separation,  at  a  certain  temperature, 
when  the  slag  is  silicious  or  calcareous  (of  low  specific 
gravity)  and  the  matte  is  high  in  copper  (of  high  specific 
gravity).  The  most  unfavorable  combination  occurs  in 
smelting  a  zinky  ore,  when  the  matte  is  bound  to  be 
mushy  and  light,  on  account  of  the  presence  of  zinc, 
and  the  slag  must  be  high  in  iron,  therefore  heavy,  in  or- 
der to  carry  off  zinc.  The  difference  in  specific  gravity 
between  matte  and  slag  is  then  small,  and  both  matte 
and  slag  are  rather  infusible. 

The  pyritic  smelters  pronounce  zinc-blende  a  good 
fuel,  but  I  have  not  found  it  to  be  a  desirable  constitu- 
ent of  the  charge  for  a  matte-smelting  furnace,  at  least 
not  for  a  small  furnace.  Blende  will  burn  fairly  well 
-in  properly  designed  kilns;  installs  the  combustion  is 
very  feeble  and  soon  ceases.  In  the  quick  descent  in  a 
blast  furnace  a  good  deal  must  escape  oxidation,  and 
difficulties  will  ensue.  There  will  be  less  trouble  if  the 
blende  be  in  small  pieces  than  if  it  be  in  large  ones ;  but 
I  should  prefer  to  have  the  blende  as  completely  oxi- 
dized outside  of  the  furnace  as  possible,  since  then  it 
will  be  easier  to  get  rid  of  in  the  slag.  There  is  a  differ- 
ence of  opinion  as  to  whether  zinc  oxide  is  carried  chem- 
ically or  mechanically  in  slag.  It  may  be  carried  in  both 
ways,  but  at  all  events  there  is  no  doubt  that  a  slag,  to 
be  high  in  zinc,  must  be  also  high  in  iron  and  low  in  sil- 

42 


WALTER  RENTON  ING  ALLS. 

ica  and  lime.  I  have  known  slags  containing  12  to  15 
per  cent  ZnO  to  be  successfully  run  in  matte  smelting, 
and  20  per  cent  ZnO  is  regularly  run  in  lead  smelting  at 
certain  places ;  but  such  slags  must  be  high  in  iron. 

The  main  difference  in  the  matte-smelting  process, 
as  now  carried  out,  lies  in  the  percentage  of  fuel  used. 
In  the  roasting-smelting  process  the  proportion  of  coke 
may  be  something  like  10  per  cent  of  the  charge ;  in  raw- 
smelting  it  may  be  about  5  per  cent.  With  coke  costing 
$10  per  ton,  there  is  then  a  difference  of  5oc.  per  ton  of 
charge  on  fuel  account,  which  will  come  to  somewhat 
more  per  ton  of  ore,  according  to  the  percentage  of  ore 
in  the  charge,  to  offset  the  cost  of  roasting.  There  is, 
on  the  one  hand,  a  greater  quantity  of  coke  to  be  han- 
dled, but  it  is  also  to  be  remembered  that  the  ore  will 
have  lost  approximately  20  per  cent  of  its  weight  in 
roasting.  The  difference  in  coke  consumption  measures 
substantially  what  is  gained  through  utilization  of  the 
maximum  fuel-value  of  the  ore.  The  matte  from  the 
raw-smelting  will  probably  be  of  lower  grade,  and  the 
cost  of  converting  it  comes  also  into  the  consideration. 

The  behavior  of  lead  in  the  matte-smelting  furnace  is 
incidentally  of  some  interest.  I  once  put  some  galena 
on  the  charge  as  an  experiment,  and  found  that  the  lead 
was  mostly  volatilized,  as  was  to  be  expected.  The  ore 
smelted  contained,  however,  regularly  a  little  lead,  0.5 
to  I  per  cent,  some  of  which  went  into  the  matte,  and  a 
little  was  reduced,  although  there  was  a  strong  oxidiz- 
ing effect  in  the  furnace.  The  metallic  lead  would  work 
down  into  the  brickwork  of  the  hearth,  and  was  extra- 
ordinarily ricii  in  gold  and  silver,  assaying  about  7  per 
cent  silver  and  from  0.5  to  2.5  per  cent  gold.  Also,  we 
found  that  the  fire-brick  would  absorb  gold  and  silver  in 
a  remarkable  way,  old  bottoms  assaying  from  150  to 
250  oz.  silver  and  8  to  20  oz.  gold.  The  brick  was  col- 
ored a  light  purple  and  was  visibly  permeated  with  met- 
allic specks  and  filaments,  probably  of  speiss.  The  use 

43 


PYRITE  SMELTING, 

of  brasque  bottoms  prevented  seepage  of  the  nch  lead, 
and  they  did  not  absorb  gold  and  silver  to  anything  like 
the  extent  the  brick  did. 

W.  R.  INGALLS. 
Boston,  Oct.  29,  1903. 


44 


CONTRIBUTION  BY  R.  L.  LLOYD. 

The  Editor : 

Sir — In  reply  to  the  ten  questions  propounded  by  the 
Journal  concerning  raw  sulphide  smelting,  I  would 
answer  as  follows : 

1.  What  types  of  ores  are  suited  to  the  process? 

Any  ore,  if  the  metals  to  be  recovered  are  gold,  silver 
or  copper,  or  all  three,  and  the  location  with  regard  to 
sulphide  favorable.  I  have  used  the  process  in  the  treat- 
ment of  dry  gold  ores,  not  amenable  at  that  time  to 
amalgamation  or  cyanide  treatment,  using  barren  py- 
rite  as  a  sulphur-carrying  material  for  a  part  of  the 
time  and  for  another  part  of  the  time  using  imported 
copper  ores,  sometimes  in  connection  with  the  barren 
pyrite  and  sometimes  without. 

2.  Is  hot  blast  advisable  ? 

I  should  say,  emphatically,  yes,  for  nearly  every  rea- 
son. It  would  almost  seem  to  go  without  question  that 
any  heat  that  can  be  imparted  to  the  blast  by  any  fuel 
cheaper  than  coke,  or  by  utilizing  waste  heat,  would 
mean  of  itself  a  clear  gain  without  taking  into  account 
other  advantages  that  are  claimed  for  hot  air,  such  as 
fast  driving,  an  increased  desulphurization,  etc.  The 
above  remark  applies,  of  course,  to  conditions  where 
fuel  is  a  matter  of  necessity;  that  is  to  say,  on  ores 
which  have  not  a  sufficient  fuel  value  of  their  own  to 
be  called  'pyritic'  ores.  With  ores  containing  a  suffi- 
cient fuel  value  of  their  own,  to  nearly  or  quite  eliminate 
the  question  of  fuel  even  under  cold-blast  conditions, 
it  would  seem  to  go  without  saying  that  heating  the 
blast  is  a  useless  expense. 

45 


PYRITE    SMELTING. 

3.  To  what  extent  can  fuel  be  eliminated  ? 

Entirely  dependent  upon  the  character  of  the  ore  and 
fuel  used.  I  believe  3  per  cent  is  as  low  as  has  been 
reported  by  any  hot-blast  furnace  running  continually. 
With  cold  blast  and  suitable  ores — that  is,  ores  contain- 
ing sufficient  heavy  sulphides — I  have  run  successfully 
for  considerable  periods  with  a  fuel  charge  as  low  as  6 
per  cent  of  the  total  burden  of  the  furnace ;  that  is,  the 
furnace  ran  on  a  charge  composed  of  94  per  cent  ore 
and  fluxes  and  6  per  cent  fuel,  a  good  Pennsylvania 
coke.  With  Butte  ores,  and  using  a  considerable 
amount  of  coarse  concentrate,  it  is  common  to  run  on 
a  charge  consisting  of  92  per  cent  ore  and  fluxes  and  8 
per  cent  coke,  wet  weights. 

4.  What  amount  of  copper  is  needed  for  the  collection  of 
the  precious  metals  ? 

A  very  reasonably  close  gold  collection  can  be  made 
with  no  copper.  A  very  good  collection  can  be  made 
with  a  charge  containing  0.3  per  cent  copper.  With 
very  high-grade  silver-gold  mattes  it  might  be  neces- 
sary to  increase  the  copper  tenor  in  the  charge  to  1.5 
or  2  per  cent.  But  if  the  matte  is  under  100  oz.  silver 
and  30  oz.  gold,  I  know  that  a  charge  having  a  copper 
tenor  of  0.5  per  cent,  or  less,  will  make  close  savings. 
At  one  time,  while  using  iron  matte  as  a  collector  for 
gold  and  silver — gold  being  the  main  value  to  be  saved 
—and  the  matte  containing  traces  only  of  copper,  our 
savings  were  97  per  cent  of  the  gold.  When  we  com- 
menced to  make  copper  matte,  using  a  charge  the  cop- 
per tenor  of  which  was  about  0.3  per  cent,  and  making 
a  very  low-grade  copper  matte  carrying  about  n  to  15 
oz.  in  gold,  our  savings  increased  to  100.5  per  cent.  This 
can  be  accounted  for  by  inaccuracies  in  assaying,  the 
gold  existing  as  telluride,  and  partially  because  the 
fluxes  used  carried  small  gold  values.  Without  chang- 
ing the  copper  tenor  of  the  charge,  we  very  often  ran 

46 


R.  L.  LLOYD. 

as  high  as  40  oz.  gold  per  ton  of  matte,  without  in  the 
least  affecting  the  cleanness  of  the  slags.  In  the  case 
above  noted,  the  silver  and  gold  were  about  equal  in 
quantity ;  that  is,  ounce  for  ounce.  As  a  matter  of  inter- 
est, I  will  say  that  we  made,  also,  at  this  time  some  very 
clean  slags  in  reverberatory  furnaces,  smelting  flue-dust 
from  the  blast  furnaces,  which  flue-dust  was  made  main- 
ly by  concentrate  from  a  large  gold  mill,  which  was  at 
one  time  our  main  source  of  sulphur.  The  resultant 
matte  from  the  reverberatorie.s  went  about  6  oz.  in  gold, 
and  the  slags  from  this  would  run  from  traces  to  20  c. 
per  ton  in  gold.  The  matte  from  these  reverberatories 
went  about  I  per  cent  copper. 

5.  W hat  percentage  of  lime  is  necessary  to  a  clean  slag"? 

This  is  dependent  entirely  vpon  the  presence  of  other 
bases,  notably  magnesia.  Magnesia,  to  a  certain  point, 
is  not  objectionable,  and,  where  metallic  bases  are  not 
to  be  had,  it  is  very  desirable  rather  than  to  carry  an  ex- 
cessively limy  slag.  We  used  magnesia  at  one  time  as 
a  very  important  part  of  our  slag,  metallic  bases  being 
unavailable,  and  dolomite  being  on  the  premises.  We 
ran  from  10  to  14  per  cent  magnesia  in  our  slags,  which 
were,  counting  alumina  as  an  acid,  bisilicates.  There 
seemed  to  be  a  distinct  relation  t  tween  the  percentages 
of  FeO  and  MgO  in  the  dag,  and  with  the  FeO  avail- 
able we  were  not  able  to  carry  over  14  per  cent  magne- 
sia successfully.  I  am  inclined,  however,  to  believe  that 
if  the  FeO  could  have  been  increased,  the  MgO  would 
have  stood  a  corresponding  increase.  I  have  made 
clean  slags  containing  5  per  cent  CaO.  These  slags 
were  quite  aluminous.  I  have  also  seen  some  very  rea- 
sonably clean  slags  containing  very  little,  or  no,  lime ; 
in  fact,  in  the  early  history  of  blast-furnace  smelting  at 
Butte,  for  a  number  of  years  our  blast-furnace  charges 
were  low  enough  in  silica  and  high  enough  in  metallic 
bases  to  require  no  outside  flux,  and  while  our  slags 

47 


PYRITE    SMELTING. 

were  not  as  clean  then  as  slags  are  made  at  this  time, 
they  were  reasonably  so,  and  could  have  been  made 
cleaner,  if  we  had  used  large  forehearths,  such  as  are 
now  commonly  used. 

6.  What  percentage  of  zinc  in  the  charge  can  be  treated 
profitably  ? 

A  proportion  of  10  per  cent  in  the  slag  is  usually 
considered  the  maximum  ZnO  for  fast  driving ;  but  this, 
and  the  percentage  of  other  objectionable  acids  or 
bases,  can  be  varied  materially,  according  to  conditions. 
For  instance,  a  coarse  charge  giving  a  high  matte-fall 
can  be  driven  faster  on  a  slag  containing  more  ZnO, 
MgO,  or  other  undesirable  acid  or  base,  than  a  charge 
which  is  fine  and  giving  a  low  matte-fall.  My  personal 
experience  with  zinky  slags  has  been  more  through  re- 
verberatory  practice  than  blast-furnace  practice,  and  I 
have  noted  that  zinky  slag  in  a  reverberatory,  that  is,  a 
slag  exceeding  10  per  cent  ZnO,  while  it  never  becomes 
as  liquid  as  a  slag  containing  an  equivalent  amount  of 
silica,  but  with  FeO  as  practically  its  own  base,  still 
smelts  at  quite  as  low  a  temperature,  and,  as  far  as  cop- 
per is  concerned,  is  quite  as  clean.  In  fact,  I  am  ac- 
quainted with  the  practice  at  one  particular  smelter  that 
habitually  makes  zinky  slags,  which  though  higher  in 
SiO2  than  the  slags  of  the  neighboring  smelters,  smelts 
at  a  lower  temperature  than  the  slags  which  have  FeO 
as  their  only  base,  calling  A12O3  an  acid  in  each  case.  I 
never  was  able  to  get  pyrometer  readings  to  check  this 
observation,  but  there  was  a  very  apparent  difference 
in  the  heats  used  at  these  works  and  those  used  by  its 
neighbors.  The  coal  per  ton  of  material  smelted  was 
also  lower  at  these  works  than  at  neighboring  smelters. 
From  the  observation  above  noted,  I  should  say  that 
ZnO  has  not  so  much  the  effect  of  lessening  the  fusing 
point  as  of  thickening  the  slag. 

48 


R.  L.  LLOYD. 

7.  What  is  the  degree  of  de sulphur ization  attainable  ? 
This  is  dependent  upon  the  original  sulphur  tenor  of 

the  ore.  With  Butte  ores  and  cold  blast,  70  to  80  per 
cent  desulphurization  is  readily  obtainable. 

8.  What  are  the  possibilities  as  to  capacity  of  furnace? 
This  is  dependent  upon  the  condition  of  the  charge 

with  regard  to  coarseness,  fineness  and  analysis,  per- 
centage of  matte-fall,  quality  of  fuel,  etc.  The  large  fur- 
naces, up  to  date,  with  very  few  exceptions,  do  not  seem 
to  drive  as  fast  per  square  foot  of  hearth  area  as  the 
smaller  furnaces.  This  also  is  true  of  reverberatory  fur- 
naces. The  larger  furnaces  make  their  savings  by  large 
tonnages,  decreased  labor  handling  successfully  more 
difficult  slags  and  with  less  fuel.  Seven  to  7.5  tons  of 
burden  smelted  per  square  foot  of  hearth  area  I  consider 
very  reasonable  work,  but  a  tonnage  considerably  in 
excess  of  this  has  been  at  times  reported. 

9.  What  are  the  limitations  of  the  process  ? 

Where  gold  and  silver  are  the  metals  aimed  at,  the 
process,  of  course,  would  be  limited  to  the  point  where 
chlorination,  amalgamation,  cyaniding  or  other  wet  pro- 
cesses could  compete,  after  the  differences  between  tail- 
ing losses  and  smelter  losses  had  been  charged  against 
milling.  Where  copper  is  the  metal  to  be  won,  the  pro- 
cess is  limited  only  by  location  and  costs,  which,  in  turn, 
depend  greatly  upon  the  analyses  of  the  ores. 

10.  What  is  the  relative  economy  as  compared  to  rival 
processes ? 

Where  the  process  is  suitable  it  has  no  successful 
rival. 

I  may  add  here  that,  in  the  above,  the  word  "we"  may 
refer  to  any  of  the  several  smelters  with  which  I  have 
been  connected  in  the  past  twelve  years. 

R.  L  LLOYD. 
Cananea,  Mexico,  Nov.  13,  1903. 

40 


CONTRIBUTION  BY  W.  T.  KEITH. 

The  Editor : 

Sir — In  the  recent  articles  on  'Raw  Sulphide  Smelt- 
ing/ published  in  The  Engineering  and  Mining  Journal, 
the  writers  have  dealt  with  the  percentage  of  cop- 
per on  the  charge  required  to  collect  the  gold  and 
silver  values  of  the  ore.  Though  the  writers  differ 
somewhat  as  to  the  requisite  quantity,  the  experiences 
of  each  are  interesting  reading,  but  I  consider  that  they 
would  be  more  instructive  if  they  had  given  some  idea 
of  the  grade  of  matte  produced. 

Does  Mr.  Lloyd  wish  to  convey  the  idea  that  with  0.5 
per  cent  copper  on  the  charge  he  can  produce,  say,  50 
per  cent  matte  in  one  concentration  and  collect  97  per 
cent  of  his  gold  values,  or  is  he  going  to  produce  a  5,  10 
or  20  per  cent  matte  ? 

I  would  like  to  ask  some  of  the  contributors  to  the 
discussion  what  percentage  of  loss  in  their  gold  value 
they  would  figure  on  making  if  they  were  concentrating 
an  ore  carrying,  say,  I  per  cent  copper,  0.5  oz.  silver  and 
o.i  2  oz.  gold  into  a  50  per  cent  matte  in  one  concentra- 
tion? 

W.  T.   KEITH. 
Greenwood,  B.  C.,  Dec.  14,  1903. 


50 


CONTRIBUTION  BY  HERBERT  LANG. 

The  Editor : 

Sir — It  is  with  pleasure  that  I  add  my  mite  to  the 
discussion  on  sulphide  smelting  that  is  proceeding  in 
your  columns,  and  which  I  have  followed  with  interest 
arid  profit.  Let  me  say  at  first  that  I  am  in  accord  with 
your  endeavors  to  find  a  more  suitable  designation  for 
this  art  than  the  somewhat  unfortunate  one  under  which 
it  now  labors,  and  if  the  usage  of  the  last  ten  years  has 
not  fixed  it  too  firmly  in  the  popular  mind  to  allow  the 
substitution  of  a  better,  I  consider  that  your  attempts 
are  well-timed  and  worthy  of  support.  The  name  'sul- 
phide' smelting  has  always  seemed  to  me  to  be  the  most 
suitable  designation,  it  having  been  used  first,  as  far  as 
I  know,  by  Mr. W.L.Austin  some  ten  years  ago.  A  year 
or  two  later  I  used  it  in  my  little  book,  'Matte  Smelting,' 
but  expressed  a  fear  then  that  the  other  name  'pyritic' 
smelting  was  too  firmly  fixed  to  permit  of  a  change. 

While  dealing  with  the  terminology  of  the  science,  I 
desire  to  suggest  the  use,  among  copper-  and  lead- 
smelters,  of  the  word  'stock/  so  much  in  vogue  among 
iron  metallurgists.  We  are  in  the  habit  of  using  such 
expressions  as  furnace  mixture,  furnace  charge,  or  ore 
mixture,  to  express  the  aggregate  of  what  is  put  into  the 
furnace.  The  one  word  'stock,'  which  to  me  has  a  fine 
old  English  ring,  covers  the  ground  much  better.  I  have 
never  noticed  its  use  in  this  connection,  in  other  than 
iron  metallurgy ;  so,  considering  the  scope  of  the  word 
and  the  accuracy  of  its  meaning,  I  think  it  would  be  a 
useful  addition  to  this  branch  of  the  science. 

i.  What  types  of  ores  are  suited  to  the  process? 

If  I  were  to  be  permitted,  I  would  modify  this  ques- 

51 


PYRITE    SMELTING. 

tion  to  read,  What  kind  of  ore  mixture  is  best  suited 
to  the  process?  For  it  makes  no  difference  what  the 
ores  are,  provided  that  their  values  are  in  gold,  silver  or 
copper,  and  that  they  do  not  contain  lead  which  it  is  an 
object  to  save.  One  ore  is  as  well  suited  to  sulphide 
smelting  as  another,  provided  that  it  be  smelted  along 
with  other  ores  or  fluxes  which  make  up  its  deficiencies 
as  a  builder  of  slag  or  matte  and  a  furnisher  of  heat. 
It  is,  therefore,  a  question,  not  of  the  composition  of  in- 
dividual ores,  but  of  the  mixture  of  ores  and  fluxes 
which  we  get  together  and  throw  into  the  furnace.  While 
an  unlimited  number  of  ores  and  mixtures  can  be  very 
well  smelted  in  the  sulphide  furnace,  the  mixture  best 
suited  to  the  process  would  consist  of  iron  pyrite,  copper 
in  some  form,  it  matters  not  what ;  silica,  at  least  partly 
in  the  free  state,  and  lime  in  the  form  of  calcite.  Each 
of  these  substances  may  be  replaced  by  many  others 
without  much  detriment  to  the  practical  work  of  the 
smelter,  but  there  are  reasons  why  these  particular  min- 
erals are  the  most  favorable.  Thus,  iron  pyrite  may  be 
replaced  by  pyrrhotite,  the  magnetic  iron  pyrite  ;  but  the 
former,  while  doubtless  containing  less  iron,  which  is  the 
combustible  par  excellence  of  this  process,  discharges  its 
sulphur  with  more  ease,  thus  getting  rid  of  a  good  pro- 
portion of  its  weight  with  but  small  expense  to  the 
smelter  for  fuel  and  blast.  Calcite,  again,  while  con- 
taining much  lime,  which  is  extremely  useful  inside  the 
furnace  in  a  variety  of  ways,  still  contains  much  carbonic 
acid,  which,  as  every  one  knows,  is  easily  gotten  rid  of 
by  merely  heating,  and,  like  sulphur,  has  no  noticeable 
effect  in  increasing  the  expenditure  of  fuel.  The  vola- 
tile ingredients  of  the  smelting  mixture,  which  pass  out 
of  the  smokestack  instead  of  entering  the  slag  and  re- 
quiring an  expenditure  of  fuel  to  fuse  and  of  labor  to 
remove,  are  in  one  sense  a  help  to  a  process  instead  of 
a  detriment.  Among  these  is  water,  and  particularly  ar- 
senic, both  of  which  are  evolved  with  ease.  Aside  from 

52 


HERBERT  LANG. 

its  tendency  to  cause  losses  of  the  precious  metals,  ar- 
senic, so  long  a  bugbear  to  other  processes,  may  be  in 
time  regarded  as  a  favorite  for  the  sulphide  process,  on 
account  of  this  easy  volatility.  I  am  not  certain  that  in 
the  list  of  desirable  substances  for  this  method  I  should 
not  put  mispickel  at  the  head,  in  place  of  iron  pyrite, 
if  it  be  a  question  merely  of  the  economical  elimination 
of  ore  constituents. 

Without  detriment  to  the  results,  there  may  be  oxid- 
ized iron  and  manganese  compounds  in  the  stock,  as 
well  as  any  kind  of  silicate  minerals  that  do  not  contain 
undesirable  bases.  It  is  not  necessarv,  as  some  think, 
that  the  stock  should  contain  a  preponderating  amount 
of  sulphides  with  merely  enough  silica  to  flux  the  iron 
that  may  be  burned.  We  do  not,  indeed,  feel  the  advan- 
tages of  the  process  until  we  have  occasion  to  smelt 
stock  which,  containing  but  a  moderate  amount  of 
pyrite,  is  so  constituted  that  a  high  concentration  is 
practicable.  In  such  a  case  we  may  perhaps  gain  more 
by  the  high  concentration  than  we  lose  by  having  to 
apply  more  coke  fuel.  This  feature  was  first  brought 
out  by  Mr.  Austin  in  the  early  days  of  the  process,  but 
does  not  seem,  even  now,  to  be  fully  appreciated  by 
those  who  practise  it. 

Under  all  circumstances  (as  I  believe)  the  sulphide- 
burning  furnace  makes  a  slag  in  which  all  the  lime,  ex- 
cepting that  small  part  that  may  become  dissolved  in  the 
slag  as  sulphide,  combines  with  the  silica  as  bi-silicate. 
The  lime,  apparently,  is  first  taken  up  by  the  silica  to 
the  exclusion  of  the  metallic  bases — iron,  zinc  and  man- 
ganese oxides — leaving  these  to  be  thereafter  satisfied 
so  far  as  the  silica  goes.  When  lime  exists  in  stock 
containing  iron  only  as  sulphide,  the  proportionate 
quantity  of  silica  requisite  to  form  the  bi-silicate  is  first 
united  with  the  lime,  when  the  remainder  of  the  silica, 
aided  by  heat  and  oxygen,  decomposes  enough  of  the 
iron  sulphide  to  produce  the  right  quantity  of  iron  oxide 

53 


PYRITE    SMELTING. 

to  flux  the  remaining  silica  and  no  more.  The  residue 
of  iron  sulphide  will  remain  unaltered,  and  will  enter  the 
matte.  It  does  not  appear  that  any  of  the  native  silicate 
minerals  which  we  find  in  ores  affect  the  iron  sulphide 
during  the  smelting,  and  it  would  probably  be  useless  to 
add  them  to  the  stock  in  the  expectation  of  their  assist- 
ing the  vital  reaction  of  decomposing  the  melted  sul- 
phide. They  may,  of  course,  be  smelted  incidentally 
to  the  process  without  assisting  in  its  characteristic  re- 
actions. This  is  true,  I  believe,  of  garnet  and  horn- 
blende, and  of  the  alumina  silicates,  manv  of  which  are 
so  common  in  ores,  particularly  in  those  of  copper. 

2.  Is  hot  blast  advisable  ? 

My  later  experience  is  altogether  favorable  to  the  hot 
blast.  I  believe  that  every  matting  blast-furnace  plant 
should  be,  and  in  time  will  be,  supplied  with  this  useful 
auxiliary.  It  is  true  that  hot  blast  complicates  the 
plant,  increasing  its  initial  cost  and  the  expense  of 
Tunning;  but  I  believe  that  it  invariably  decreases  the 
cost  of  treating  the  ore.  At  least,  I  do  not  know  of  a 
single  plant  where  it  has  not  done  so  when  used.  When 
the  pyritic  process  was  first  advocated,  many  mistaken 
ideas  were  prevalent  as  to  the  functions  of  the  hot  blast. 
Some  maintained  that  the  process  could  not  go  on  with- 
out it,  holding  that  the  previous  heating  of  the  air  was 
a  sine  qua  non.  It  is  said  that  I  was  the  first  to  demon- 
strate that  there  was  such  a  thing  as  cold-blast  pyritic 
smelting,  which  is  something  that  we  see  going  on  every 
day  now.  This  unimportant  fact,  which  I  hope  to  be 
excused  for  citing,  does  not  blind  me  to  the  advantages 
of  heating  the  blast,  which  I  have  long  been  in  the  habit 
of  advocating.  As  I  see  it,  the  heating  of  the  blast 
assists  in  different  ways.  First,  it  saves  fuel  (ques- 
tion 3) ;  this  cannot  be  denied  by  even  the  most  hide- 
bound of  our  opponents — if  we  have  any  opponents  at 
this  late  day.  Second,  it  makes  the  furnace  drive  faster 

54 


HERBERT  LANG. 

and  smelt  more.  This  may  be,  and  has  been,  disputed, 
but  I  maintain  it  in  the  face  of  the  assertions  to  the  con- 
trary, which  come  from  high  sources.  In  my  personal 
experience  such  has  always  been  the  case.  I  have 
studied  the  process  closely  for  a  dozen  years  and  more, 
and  have  never  missed  an  opportunity  to  investigate  its 
peculiarities ;  and  I  repeat  that,  under  all  circumstances 
with  which  I  am  familiar,  the  hot  blast  has  increased  the 
rate  of  driving  very  materially.  It  is  natural  that  it 
should  do  so,  for,  as  less  fuel  is  required,  the  lessened 
amount  will  be  consumed  quicker,  and  will  permit  the 
descent  of  the  charges  much  faster,  this  resulting 
directly  in  increasing  the  capacity  of  the  furnace.  It 
takes  a  certain  amount  of  time  and  of  air  to  burn  coke, 
and  the  more  coke  the  more  time  and  air.  This  is 
demonstration  enough  for  the  ordinary  man,  and  when 
I  add  to  this  the  observed  fact  that  the  furnaces  that  I 
have  known  actually  ran  faster  with  hot  blast  than  with 
cold,  I  feel  that  I  have  had  my  say. 

At  a  time  when  metallurgists  had  at  command  no 
other  apparatus  for  blast  heating  than  the  cast-iron 
pipe-stoves  of  a  past  era,  hot  blasts  were  not  so  often 
advisable.  The  stoves  of  which  I  speak  were  adopted 
bodily  from  the  iron  regions  of  the  East,  and  had  three 
defects,  which  rendered  them  ineffective  to  a  great  de- 
gree. They  were  extravagant  in  first  cost;  they  im- 
peded the  blast;  and,  finally,  they  were  very  inefficient 
in  the  matter  of  heat  transference.  Stoves  of  this  pat- 
tern are  known  to  impede  the  blast  in  its  passage  to 
such  an  extent  that  the  pressure  at  the  blower  com- 
monly registers  from  6  to  16  oz.  more  than  at  the 
tuyeres,  showing  a  great  loss  in  power  and  pressure. 
The  cause  is  that  the  passages  are  much  too  tortuous 
and  constricted.  The  apparatus  is  usually  gotten  up  on 
the  original  plans  of  some  extinct  iron  works,  without 
any  alteration  to  meet  the  much  lower  pressures  used 
in  copper  smelting.  I  do  not  know  that  any  one  has 

55 


PYRITE    SMELTING. 

ever  executed  tests  showing-  the  heat  applied  to  and 
returned  by  such  stoves,  so  I  cannot  speak  from  accu- 
rate knowledge;  but  I  do  not  imagine  that  any  such 
stove  has  an  efficiency  of  more  than  50  per  cent,  if  as 
much.  With  such  apparatus  as  this,  it  is  no  wonder 
that  operators  have  sometimes  felt  that  the  hot  blast 
was  not  always  advisable.  I  notice  from  the  lately  pub- 
lished reports  of  the  operations  at  Mt.  Lyell  that  the 
stoves  there,  when  heating  the  blast  to  500°  F.,  had  an 
efficiency  of  49  per  cent,  according  to  my  own  esti- 
mates, based  on  their  data,  and  assuming  an  average 
calorific  power  for  the  wood  with  which  thev  are  heated ; 
and  that  they  retarded  the  blast  to  such  an  extent  that 
the  pressure  at  the  furnaces  was  6  oz.  per  sq.  in.  below 
that  at  the  blowers,  thus  consuming  about  one-sixth  of 
the  power  applied  to  the  latter.  Surely,  there  is  no  rea- 
son for  the  tone  of  gratulation  in  which  interested  par- 
ties speak  of  the  performances  of  these  particular 
stoves. 

3.  To  what  extent  can  fuel  be  eliminated  ? 

The  saving  of  fuel  in  the  process  under  consideration 
varies  much  with  different  charges  and  conditions.  Un- 
less we  use  the  hot  blast,  there  is  no  saving-  of  fuel  in 
particular.  With  it,  we  save  from  one-half  to  two- 
thirds  of  what  would  be  used  without  it.  Thus,  if  the 
charge  required  10  per  cent  of  coke  to  smelt  with  the 
cold  blast,  it  would  probably  require  from  3  to  5  per 
cent  with  the  heated  blast.  This  would  depend  some- 
what upon  the  composition  of  the  charge,  and  especially 
as  to  its  contents  in  sulphides,  which  furnish  the  prin- 
cipal fuel.  One  smelter  that  I  know  of  is  regularly 
treating  sulphide  mixtures  with  6  per  cent  of  coke  with 
cold  blast.  While  its  stock  is  well  adapted  to  hot-blast 
smelting,  it  is  not  possible  to  save  much  fuel  by  its  aid, 
the  present  consumption  being  so  small.  In  all  such 

56 


HERBERT  LANG. 

cases  where,  with  cold  blast,  a  low  fuel  consumption  is 
claimed,  we  must  expect  to  find  a  quite  low  degree  of 
concentration.  Such  is  the  case  at  the  works  of  which 
I  speak.  Cases  are  known  where  no  carbonaceous  fuel 
at  all  is  used,  the  whole  supply  of  heat  arising  from  the 
comb.ustion  of  sulphides  and  from  the  hot  air  blown  in. 
The  latter  source  of  heat  may  also  be  eliminated,  it  is 
claimed,  and  the  sulphides  relied  upon  solely.  It  is  said 
that  at  Mt.  Lyell,  where  for  years  they  heated  the  blast 
to  some  500°  and  a  little  more,  the  tendency  now  is  to 
blow  harder  and  heat  the  blast  less,  and  rely  almost 
entirely  on  the  combustion  of  the  sulphides  for  the  heat. 
We  cannot  tell  to  what  these  new  experiments  may 
lead;  but  it  is  hardly  in  the  line  of  economy  to  spend 
much  money  on  a  heavier  blast  without  first  inquiring 
if  the  useful  effects  of  a  hotter  and  lighter  one  may  not 
be  preferable  and  had  at  a  cheaper  rate. 

4.  What  amount  of  copper  is  needed  for  the  collection  of 
the  precious  metals  ? 

This  question  refers,  I  suppose,  to  the  quality  of  the 
matte  which  is  produced.  The  aggregate  amount  of 
copper  in  the  ore  would  not  be  a  pertinent  matter.  It  is 
the  richness  of  the  matte  that  tells  the  story.  I  have 
always  found  a  matte  of  from  30  to  50  per  cent  of 
copper  to  give  the  best  results  in  a  high  percentage  of 
extraction  of  gold  and  silver.  Others  have  had  a  dif- 
ferent experience,  and  some  even  claim  that  copper  is 
unnecessary  in  the  matte.  My  impression  is  that,  if  the 
slag  accompanying  the  matte  be  largely  composed  of 
lime  or  magnesia,  the  iron  matte  without  copper  will 
serve  as  a  collector;  but  that  with  a  heavv  iron  slag, 
such  as  falls  when  the  charge  is  high  in  pyrite,  a  coppery 
matte  is  essential.  It  really  requires  but  a  very  little 
matte  to  extract  the  values  if  it  be  of  the  right  sort; 
nor  have  I  found  a  large  proportion  of  matte,  of  what- 
ever composition,  to  have  any  effect  in  reducing  the 

57 


PYRITE    SMELTING. 

slag  losses.  A  singular  notion  is  prevalent  among  sev- 
eral metallurgists  who  have  addressed  you  of  late.  They 
appear  to  think  that  successful  smelting  cannot  be  done 
unless  a  certain  proportion  of  matte  be  made,  some 
putting  the  quantity  as  high  as  10  or  15  per  cent.  One 
says  that  the  tuyeres  get  dark ;  another,  that  the  hearth 
fills  up,  etc.,  etc.  The  small  proportion  of  matte,  in- 
deed, is  not  without  its  influence  on  the  working  of  the 
furnace,  but  even  if  the  matte-fall  ceases  entirely  the 
smelting  will  proceed,  perhaps  unchecked.  Let  me  ask 
such  operators  if  they  can  smelt  charges  of  slag  alone, 
where  no  matte  is  produced ;  or  if  they  have  ever  tried 
to  handle  mixtures  giving  a  concentration  as  high  as 
20  and  even  40  to  one. 

Question  5,  which  asks  what  percentage  of  lime  is 
necessary  to  a  clean  slag,  leads  naturally  to  the  wider 
question  of  the  influence  of  lime  on  slag  losses.  Lime  is 
exceedingly  beneficial  in  the  furnace  for  three  reasons 
at  least,  which  I  may  dwell  upon.  In  the  first  place, 
the  lime-slags  of  the  composition  indicated  before,  work 
extremely  well  in  the  blast-furnace.  They  run  very 
nicely,  with  a  smooth,  oily  flow,  do  not  sputter,  and  keep 
the  furnace  and  its  accessories  in  first-rate  condition. 
They  are  light  and  reasonably  fluid,  and  allow  the  matte 
globules  to  settle  out  most  perfectly.  Any,  even  the 
lightest,  iron  matte  will  settle  from  high  lime  slags.  It 
seems  to  me,  when  I  consider  the  behavior  of  these  ad- 
mirable substances,  that  a  pure  bi-silicate  of  lime  would 
have  no  action  at  all  upon  entangled  sulphides.  The  ex- 
pression "clean  slag"  is  a  relative  one.  There  is  no 
such  thing  as  a  slag  entirely  free  from  gold,  silver  and 
copper ;  but  I  think  that  the  high-lime  slags  come  near- 
est to  absolute  cleanness.  Of  all  such  slags,  those  con- 
taining nearly  an  equal  amount  of  bi-silicate  of  lime  and 
singulo-silicate  of  iron  behave  the  best,  all  things  con- 
sidered, and  will  be  as  clean  as  we  can  get.  Lime  is  not 
often  a  constituent  of  sulphide  ores,  so  that  we  can 

58 


HERBERT  LANG. 

hardly  expect  it  to  enter  largely  into  slag  composition 
in  this  form  of  smelting;  nor  is  it  entirely  necessary 
that  it  should.  Quite  acceptable  slags  are  made  with 
iron  oxide  as  almost  the  sole  base.  I  have  made  such, 
and,  regarding  their  freedom  from  valuable  metals,  I 
recall  that  the  average  proportion  of  copper  carried  off 
by  them  at  one  works  was  nearly  0.5  per  cent,  which  is 
probably  twice  as  much  as  a  well-constituted  lime-iron 
slag  would  have  shown.  However,  under  the  existing 
circumstances,  this  result  was  good.  It  would  not  have 
paid  to  add  lime  to  such  a  slag  unless  it  could  have 
been  secured  in  the  form  of  a  paying  ore,  which  at  that 
locality  was  impossible.  Speaking  generally,  and  with- 
out reference  to  particular  localities,  I  should  say  that 
it  would  never  pay  to  add  lime  to  pyritic  charges  when 
iron  in  any  form  can  be  had  at  less  cost.  On  the  other 
hand,  it  would  never  pay  to  add  iron  oxide  as  flux  when 
lime  ores  can  be  had  at  less  cost,  provided  that  the  per- 
centage of  lime  does  not  surpass  30  or  thereabouts ;  for 
a  slag  containing  much  above  this  percentage  will  not 
melt  properly  in  the  cupola. 

The  degree  of  desulphurization  in  the  furnace,  de- 
pending as  it  does  upon  a  large  number  of  factors,  is 
very  variable.  When  the  stock  consists  mainly  of  heavy 
pyritous  ore,  where  it  is  not  practicable  to  flux  highly 
with  silica,  the  proportion  of  sulphur  expelled  will  be 
small,  perhaps  not  more  than  60  or  70  per  cent.  When 
the  ores  contain  any  other  bases  than  iron,  and  especi- 
ally when  they  contain  much  lime  (and  probably  mag- 
nesia), mingled  proportionally  with  silica,  the  combus- 
tion of  sulphides  is  more  extensive,  and  frequently  as- 
cends to  80  per  cent  and  more.  When  treating 
charges  of  mixed  ores,  oxides  and  sulphides  with  a  sul- 
phur content  of  8  or  10,  I  noticed  that  75  per  cent  of 
the  sulphur  was  expelled.  Mixtures  carrying  26  to  28 
per  cent  gave  the  same  result,  but  would  have  lost  more 
had  the  fluxes  been  suitable  for  the  work.  On  another 

59 


PYRITE    SMELTING. 

occasion,  when  smelting  a  mixture  containing  some  1 1 
per  cent  sulphur,  the  percentage  driven  off  reached  the 
extraordinary  figure  of  96  per  cent.  The  result  in  this 
case  was  due,  in  my  opinion,  to  the  two  concurrent  facts 
that  the  ore  carried  nearly  as  much  arsenic  as  sulphur, 
while  the  flux  consisted  of  a  large  proportion  of  lime, 
which  is  observed  to  influence  the  expulsion  of  sulphur 
— and  hence  concentration  of  the  product — in  a  very 
favorable  manner.  The  arsenic,  as  I  observed,  was 
largely  sublimed  in  the  form  of  a  sulphide,  and  to  this  I 
mainly  ascribe  the  good  results  obtained  during  the 
smelting.  Others  have  noticed  that  at  certain  times, 
depending  on  the  condition  of  the  furnace,  all  the  sul- 
phur may  be  burned  off  from  charges  low  in  that  ele- 
ment. 

10.  What  is  the  relative  economy  as  compared  to  rival 
processes ? 

This  question  I  find  most  difficult  to  answer.  In  fact, 
I  do  not  think  that  it  can  be  satisfactorily  answered  in 
general  terms.  It  would  be  necessary  to  study  the 
conditions  that  surround  each  individual  case  in  order 
to  form  a  judgment  as  to  the  applicability  or  economy 
of  this  or  that  process.  As  I  have  heretofore  said, 
there  are  no  ores  whatever  of  silver,  gold  or  copper 
which  may  not  be  treated  by  sulphide  smelting  if  the 
stock  be  proportioned  right,  but  there  are  thousands 
of  cases  where  some  other  process  may  prove  more 
economical.  In  the  matter  of  general  availability, 
there  is  no  doubt  that  sulphide  smelting  has  a  great 
advantage  over  all  others.  Again,  it  is  advantageous 
in  that  no  process  requires  so  little  preliminary 
preparation  of  the  stock.  This  fact  makes,  of  course, 
for  economy  in  running,  and  particularly  for  the  general 
usefulness  of  the  process.  The  plant  itself  is  cheap  and 
simple,  and  if  well  constructed  is  at  least  as  reliable  in 
its  work  as  the  lead  process  or  any  other  well  known 

60 


HERBERT  LANG. 

method.  I  have  noticed,  however,  a  tendency  to  put 
up  cheap  and  trivial  plants,  which  is  much  to  be  re- 
gretted, as  it  will  inevitably  tend  to  retard  the  develop- 
ment of  the  process. 

In  considering  the  merits  of  a  process,  we  must  not 
blind  ourselves  to  its  disadvantages.  The  principal 
drawback  of  sulphide  smelting,  by  which  its  economy 
is  much  lessened  as  compared  with  other  methods,  lies 
in  its  production  of  a  crude  and  comparatively  unfin- 
ished end-product,  which  is  not  only  heavy  and  burden- 
some to  handle  and  transport,  but  requires  costly  and 
complex  operations  to  bring  into  useful  form.  The  same 
is  true  of  the  ordinary  plain  matting  processes.  As 
compared  with  these,  such  methods  as  chlorination  and 
amalgamation,  whose  end-products  are  saleable  at  the 
mine,  have  an  advantage  which  must  not  be  overlooked. 
As  regards  the  cost  of  treatment,  now  one,  now  another 
process  has  the  advantage ;  but,  as  a  matter  of  fact,  the 
improvements  of  late  years  have  brought  down  the  cost 
in  all  the  standard  processes  to  so  low  a  pitch  that  there 
is  often  not  enough  difference  between  them  to  incline 
the  judgment  either  way.  It  would  seem  that  nobody 
is  building  plants  nowadays  with  the  expectation  of  their 
costing  over  $3  or  so  per  ton  for  treating  the  ore  or 
stock.  I  speak  now  of  the  larger  establishments  which 
are  springing  up  so  numerously  on  our  western  hillsides. 
In  forming  our  ideas  in  the  matter  of  costs  of  treat- 
ment, we  must  not  omit  to  discriminate  between  the 
amount  and  character  of  the  preliminary  preparation  re- 
quired to  fit  the  ore  to  the  process  to  be  applied,  and 
which  frequently  makes  quite  an  item  to  be  added  to  the 
total  of  expenses,  although  in  this  comparison  I  have 
not  considered  it  as  belonging  strictly  to  the  process. 
Thus  roasting  is  in  no  sense  a  part  of  the  lead-smelting 
process,  but  is  sometimes  a  necessary  preliminary 
thereto,  as  it  is  to  chlorination  in  most  of,  if  not  quite 
all,  cases,  and  to  cyanidation  in  many. 

61 


PYRITE    SMELTING. 

Numerous  instances  have  been  cited  in  print  where 
the  cost  of  treatment  has  been  brought  as  low  as  $2  per 
ton,  and  in  the  case  of  matting  and  stamp  amalgama- 
tion to  $i.  What  wonderful  progress  these  facts  indi- 
cate! I  well  remember  the  time  when  men  went  broke 
trying  to  smelt  for  $50  and  $100  per  ton. 

HERBERT  LANG. 
Oakland,  Cal.,  Dec.  7,  1903. 


CONTRIBUTION  BY  L.  D.  GODSHALL. 

The  Editor : 

Sir — The  discussion  of  this  subject  by  different  metal- 
lurgists cannot  help  but  be  of  importance  equal  to,  if 
not  greater  than,  the  recent  interesting  and  valuable  dis- 
cussions on  mine  sampling  and  ore  deposition. 

The  subject  at  the  present  time  seems  to  be  in  a  con- 
dition somewhat  similar  to  that  of  the  cyanide  process 
at  the  time  of  its  early  introduction  into  this  country. 
During  the  last  ten  years  much  has  been  written  upon 
the  subject  of  pyritic  smelting.  Many  plants  have  been 
put  in  operation  and  a  record  of  failures  has  resulted, 
fully  equal  to  that  of  the  early  attempts  at  cyanidation. 
•Until  quite  recently  it  has  been  very  difficult  to  obtain 
reliable  information  of  actual  results  secured  in  prac- 
tical work.  Most  extravagant  claims  frequently  have 
been  made,  and  are  still  forthcoming,  concerning  the 
superiority  of  this  method  of  smelting  over  any  other. 
On  the  other  hand,  important  improvements  and  dis- 
coveries also  have  been  made  during  recent  years. 

We  have,  therefore,  on  account  of  these  advances  and 
in  spite  of  many  failures,  every  reason  to  hope  that  in 
the  near  future  matte  smelting,  together  with  its  modi- 
fication, pyritic  smelting,  will  become  as  important  in 
fire  metallurgy  as  cyanidation  is  now  in  the  wet  treat- 
ment of  ores. 

In  order  to  bring  out  as  full  a  discussion  on  this  sub- 
ject as  possible  I  shall  criticize  rather  freely  such  state- 
ments and  claims  as  in  my  opinion  are  either  not  borne 
out  by  experience  or  else  not  sufficiently  clearly  pre- 
sented to  be  correctly  understood.  I  shall  also  call 
attention  to  some  statements  and  results  obtained 


PYRITE    SMELTING. 

which,  in  my  opinion,  are  of  the  greatest  importance. 
Certain  statements  and  data  have  been  taken  from  a 
publication  or  catalogue  issued  by  the  Colorado  Iron 
Works,  of  Denver,  the  accuracy  of  which  has,  however, 
been  vouched  for  by  Mr.  J.  W.  Nesmith,  president  of  the 
company. 

In  this  connection  I  wish  to  say  that  I  am  seeking  for 
reliable  information,  no  matter  whether  obtained  from 
practical  furnace  foremen,  who  have  never  seen  the  in- 
side of  a  technical  institution ;  reliable  manufacturers  of 
smelting  machinery,  perhaps  equally  devoid  of  tech- 
nical training,  but  constantly  in  touch  with  metallurgists 
and  smelting  men  in  many  different  localities  and  work- 
ing under  as  many  different  conditions ;  highly  educated 
but  practically  inexperienced  professors  of  metallurgy 
or  practically  experienced  and  technically  trained  metal- 
lurgists. 

Your  editorial  in  the  issue  of  October  10  defines  the 
above  subject  as  follows :  "Raw  sulphide  smelting  may 
be  defined  as  the  treatment  of  unroasted  sulphide  ores 
with  a  view  to  the  formation  of  a  matte."  And  "Raw 
sulphide  smelting  is  based  upon  the  utilization  of  the 
heat  derived  from  the  combustion  of  sulphide  ores  in  a 
blast  furnace  in  contradistinction  to  the  heat  obtained 
directly  from  carbonaceous  fuel."  (The  italics  are 
mine.) 

You  appear  to  object  to  the  well-known  terms  pyritic 
smelting  and  matte  smelting,  claiming  that  these  terms 
do  not  cover  the  ground.  The  former  is  said  to  omit 
pyrrhotite  ores  and  the  latter  to  include  roasted  ores. 
These  objections,  it  seems  to  me,  are  due  altogether  to 
the  view  one  takes  of  the  scope  of  the  terms  used.  As  I 
understand  the  term  'pyritic'  smelting,  pyrrhotite  ores 
are  not  omitted,  while  the  fact  that  matte  smelting  does 
include  the  treatment  of  roasted  ores  should  be  in  its 
favor,  as  being  more  comprehensive. 

Mr.  Ingalls  notes  some  objections  to  the   term  'raw 

64 


L.  D.  GODSHALL. 

sulphide'  smelting.  These  I  consider  well  taken.  In 
my  opinion,  however,  he  has  omitted  to  state  some  of 
the  strongest  objections.  Among  these  are  the  con- 
ditions governing  the  smelting  of  various  ores  where 
the  contents  in  sulphur  are  so  low  that  it  becomes  neces- 
sary to  maintain  a  reducing  atmosphere  in  smelting,  in 
order  to  prevent  the  small  amount  of  sulphur  present 
from  being  oxidized  and  to  obtain  the  copper  in  a  matte 
form,  and  at  the  same  time  to  produce  enough  of  the 
latter  to  collect  the  gold  and  silver  values  present  in  the 
ore. 

If  the  definition  and  basis  of  utilization  of  heat  be  ac- 
cepted as  above  given,  we  can  at  this  time  have  only  a 
modification  of  'raw  sulphide'  smelting  in  America,  be- 
cause at  no  place,  so  far  as  I  know,  is  carbonaceous  fuel 
entirely  eliminated. 

In  order  to  induce  further  discussion  on  this  point, 
therefore,  I  make  the  following  suggestions :  To  stick 
to  our  old  terms  of  'lead  smelting/  'copper  smelting/ 
and  'matte  smelting.'  We  are  all  familiar  with  the 
many  different  variations  in  the  processes  of  the  two 
former,  and  let  us  accept  and  define  those  of  the  latter. 
It  is  true  that  copper  smelting  gradually  merges  into 
matte  smelting,  but  the  latter  covers  more  cases  uni- 
versally regarded  as  distinct  from  copper  smelting  than 
either  'pyritic'  or  'raw  sulphide'  smelting. 

I  would  suggest  that  the  definition  and  basis  be  some- 
what changed  to  read  as  follows :  Matte  smelting  may 
be  defined  as  the  treatment  of  various  ores  with  a  view 
to  collecting  the  different  values  by  means  of  a  matte 
produced ;  and,  Matte  smelting  is  based  upon  the  utili- 
zation of  the  heat  derived  from  combustion  of  sulphide 
ores  in  a  blast  furnace,  in  addition  to  the  heat  obtained 
directly  from  carbonaceous  fuel.  The  basis,  as  here 
stated,  therefore,  includes  such  variations  as  will  result 
from  the  minimum  of  heat  derived  from  the  combustion 
of  sulphide  ores  in  the  case  of  roasted  ores,  and  raw  ores 

65 


PYRITE    SMELTING. 

very  low  in  sulphur  contents,  to  the  maximum  of  heat 
derived  from  such  combustion  in  the  case  of  heavy  raw 
sulphide  ores,  as  smelted  at  Mt.  Lyell,  Salt  Lake,  and 
other  places. 

Pyritic  smelting  now  becomes  a  branch  or  part  of 
matte  smelting,  and  may  be  defined  as  follows :  Pyritic 
smelting  is  a  form  of  matte  smelting  whereby  the  maxi- 
mum amount  of  heat  is  derived  from  the  combustion  of 
heavy  raw  sulphide  ore  in  a  blast  furnace,  in  addition  to 
the  minimum  amount  of  necessary  heat  obtained  directly 
from  carbonaceous  fuel. 

All-  types  of  ore,  suitable  for  copper  smelting,  are 
equally  so  for  matte  smelting,  with  the  possible  excep- 
tion of  high-grade  oxidized  ores  of  copper  under  con- 
ditions suitable  for  direct  smelting  to  black  copper.  In 
addition  to  the  above,  all  kinds  of  dry  ores,  together 
with  ores  carrying  a  limited  amount  of  lead  and  zinc, 
the  limit  of  the  former  being  a  question  of  commercial 
value  of  the  lead  lost  as  compared  with  the  cheaper  re- 
duction of  the  other  metals  contained  in  the  ore. 

The  limit  of  the  zinc  ought  to  be  such  that,  when 
mixed  with  the  charge,  the  normal  amount  of  ZnO  con- 
tained in  the  slag  shall  be  about  8  per  cent,  with  a  maxi- 
mum of  10  per  cent.  Higher  zinc  slags  have  been  run, 
according  to  Mr.  Ingalls,  but  in  the  opinion  of  the  writer 
any  increase  on  the  above  percentages  will  bring  many 
difficulties  in  connection  with  the  operation  of  the  fur- 
nace, in  addition  to  a  largely  decreased  capacity  re- 
sulting therefrom. 

The  amount  of  sulphur  on  the  charge  may  vary  from 
the  maximum  amount  present  with  the  iron  as  FeS2  to 
a  minimum  of  3  per  cent,  provided  the  percentage  of 
copper  remains  slightly  less. 

So  far  as  I  know  there  are  to-day  no  slags  made  by 
matte  or  pyritic  smelters  which  are  not  closely  or 
exactly  duplicated  by  the  copper  smelters.  This  kind 
of  smelting  is  therefore  not  distinct  from  copper  smelt- 

66 


L.  D.  GODSHALL. 

ing  on  account  of  any  difference  in  the  slags  to  be  ob- 
tained, but  it  is  rather  a  process  using"  a  greater  variety 
of  ores  and  obtaining  similar  slags  with  different 
methods. 

The  question  of  the  advisability  of  using  a  hot  blast 
is  a  most  important  one ;  and,  in  addition  to  its  import- 
ance, there  is  at  the  present  time  also  the  greatest  dif- 
ference of  opinion  as  to  its  economy  among  metal- 
lurgists engaged  in  this  branch  of  smelting.  In  order 
to  discuss  this  question  intelligently,  it  is  necessary  to 
start  from  a  common  understanding  of  the  word  "ad' 
visable."  In  my  opinion  in  this  connection  it  must 
mean  that  it  is  more  economical  and  therefore  more 
profitable  to  use  a  hot  than  a  cold  blast  in  smelting. 

With  the  claims  and  evidence  for  and  against  this 
proposition,  it  becomes  necessary  to  study  closely  the 
conditions  present  as  well  as  the  results  obtained  in  con- 
nection with  both  cases. 

Very  strong  claims  have  been  made  by  hot-blast  ad- 
vocates concerning  its  superiority  over  cold  blast. 
Koch1  claims  that  a  blast  of  200°  C.  produced  cleaner 
slags  with  wider  range  and  smoother  work.  Mathew- 
son2  claims  that  hot  blast  will  produce  higher  grade 
matte,  or,  in  other  words,  that  it  will  oxidize  more  sul- 
phur than  its  equivalent  of  cold  blast.  Austin3  claims  it 
is  advantageous  in  smelting  a  silicious  or  infusible 
charge.  Bretherton4  cites  many  advantages,  among 
them,  increased  capacity  of  furnace,  saving  of  fuel, 
brighter  tuyeres,  smoother  running  of  furnace,  largely 
increased  limit  of  zinc  and  arsenic  on  charge  by  reason 
of  its  stronger  oxidizing  action,  and  concludes  with  the 
statement  that  hot  blast  reduces  the  cost  of  smelting 
nearly  half  on  heavy  sulphide  ore.  Lloyd5  claims  in- 
creased capacity,  stronger  oxidizing  action,  and  that  it 
is  cheaper  to  heat  the  blast  before  it  enters  the  furnace 
than  to  heat  it  in  the  furnace  with  coke.  J.  W.  Nes- 

iSee  page  24.    2See  page  21.    3See  page  17.    4See  page  28.    59ee  page  45. 

67 


PYRITE    SMELTING. 

mith,  as  a  manufacturer  of  blast  furnaces,  claims  two 
points  in  favor  of  the  hot  blast:  A  saving  of  at  least 
10  per  cent  in  the  cost  of  the  fuel  used  per  ton  of  ore 
smelted,  and  an  increased  smelting  capacity  of  at  least 
25  per  cent. 

The  claims  above  enumerated  in  favor  of  the  hot  blast 
cannot  be  ignored.  If  only  a  part  of  them  can  be  sub- 
stantiated, the  value  of  the  hot  blast  must  be  admitted. 

The  evidence  on  the  opposite  side  is  mainly  of  a  nega- 
tive character,  and  consists  principally  in  a  failure  on 
the  part  of  metallurgists  of  note  to  find  the  merits 
claimed  for  the  hot  blast.  Carpenter1  says  he  "has 
never  found  the  magic  in  mere  hot  air  that  others  have 
professed  to  find."  Pre-eminently  the  greatest  ex- 
ponent of  the  hot  blast  is  Sticht  in  his  practical  experi- 
ence at  Mt.  Lyell,  where  he  is  using  it  with  such  un- 
qualified success.  In  contrast  with  his  experience,  we 
have  that  of  Nutting,  at  the  Bingham  smelter  at  Salt 
Lake,  and  Carpenter  at  Deadwood.  The  former  is 
working  under  conditions  as  nearly  identical  with  those 
at  Mt.  Lyell  as  it  is  possible  to  find ;  the  latter,  at  Dead- 
wood,  under  conditions  as  widely  different.  Both  use 
cold  blast,  and  the  scope  and  commercial  success  of 
Nutting  apparently  is  on  an  equality  with  that  at  Mt. 
Lyell.  In  addition  to  the  practical  experience  of  these 
two  prominent  operators,  we  have  that  of  Butte,  where 
hot  blast  has  been  tried  without  apparent  success.  An 
examination  of  the  actual  results  obtained  at  different 
plants  using  the  hot  and  cold  blast  now  becomes  inter- 
esting. 

In  all  cases,  so  far  as  I  know,  where  heavy  raw  sul- 
phide ores,  low  in  copper,  are  smelted  without  a  pre- 
liminary roasting,  a  double  smelting  is  required  in  order 
to  obtain  a  matte  sufficiently  high  in  copper,  say  from 
45  to  5°  Per  cent>  f°r  converter  purposes.  This  applies 

i  See  page  83. 


L.  D.  GODSHALL. 

alike  to  hot-  and  cold-blast  smelting.  At  Mt.  Lyell  the 
grade  of  the  first  matte  is  said  not  to  exceed  15  per  cent 
copper,  being  a  concentration  of  about  seven  tons  of 
original  ore  into  one  ton  of  matte.  Higher  grade  first 
mattes  are  being  produced  at  other  places,  but  with  a 
lower  percentage  of  sulphur  on  the  charge.  At  the 
Bingham  plant  at  Salt  Lake,  where  the  character  of  the 
charge  is  similar,  but  cold  blast  is  used,  I  have  been 
informed  from  unofficial  sources  that  the  grade  of  the 
first  matte  is  also  about  15  per  cent  copper. 

The  products  of  the  hot  and  cold  blast  do  not,  there- 
fore, seem  to  show  any  great  difference,  from  which  we 
may  conclude  that  on  certain  classes  of  ore  the  oxidiz- 
ing action  of  the  hot  blast  does  not  seem  to  exceed  that 
of  the  cpld  blast.  On  ores  containing  appreciable 
quantities  of  zinc,  lead,  arsenic  or  antimonv,  or  on  first 
mattes,  where  the  sulphur  is  less  easily  oxidized,  more 
information  is  necessary  before  any  definite  decision 
on  the  relative  efficiency  in  oxidizing  action  between 
the  hot  and  cold  blast  can  be  reached.  Bretherton 
claims  to  have  obtained  a  higher  oxidizing  action  with 
the  hot  blast  in  connection  with  zinc  sulphide,  but  gives 
no  figures.  He  also  states  that  the  elimination  of  ar- 
senic so  far  has  not  been  successfully  accomplished  with 
cold  blast. 

The  last  statement  requires  modification,  as  it  is  well 
known  how  simple  and  easy  it  is  to  volatilize  the  arsenic 
when  present  as  arsenical  pyrite.  The  writer  has  even 
added  speiss  in  large  quantity  and  in  large  pieces  to 
matte  smelting  charges,  using  cold  blast  under  oxid- 
izing conditions,  without  discovering  any  evidence  of 
the  presence  of  arsenic  in  the  matte  produced.  The 
speiss  in  question  had  been  produced  in  lead  smelting. 
Practical  results  obtained  in  the  concentration  of  first 
matte  by  hot-  and  cold-blast  smelting  would  shed  con- 
siderable light  on  the  subject.  Until  such  information 

69 


PYRITE    SMELTING. 

is  forthcoming,  it  seems   as  if    the  greater    oxidizing 
action  claimed  for  the  hot  blast  is  yet  unproved. 

The  comparative  furnace  capacity  is  difficult  to  de- 
termine. We  have  so  many  cases  of  phenomenal  ca- 
pacity obtained  with  the  cold  blast,  both  in  copper  and 
in  matte  smelting,  that  it  is  difficult  to  imagine  any 
greater  efficiency  with  the  aid  of  the  hot  blast.  Mr. 
Paul  Johnson,  the  pioneer  in  copper  and  matte  smelting 
in  British  Columbia,  obtained,  at  Nelson  and  in  the 
Boundary  district,  results  in  capacity  with  the  cold  blast 
not  excelled  at  any  place  with  the  hot  blast.  Mr.  Robert 
Hedley,  who  succeeded  Mr.  Johnson  at  Nelson,  has 
been  equally  successful  with  cold-blast  work.  The 
slags  made  there  were,  moreover,  what  are  usually 
termed  highly  silicious,  containing  about  42  per  cent 
silica,  and  from  15  to  20  per  cent  alumina,  the  charge 
containing  but  from  2  to  5  per  cent  copper,  besides 
some  silver  and  gold.  The  matte  produced  in  one 
smelting  assayed  from  45  to  50  per  cent  copper,  the 
slags  from  0.2  to  0.3  per  cent  in  copper,  and  as  clean 
from  silver  and  gold  as  in  lower  concentration.  The 
capacity  of  the  furnace  was  frequently  in  excess  of  300 
tons  per  day  and  seldom  below  250  tons. 

At  Butte  and  Great  Falls,  as  well  as  at  other  places, 
capacities  with  the  cold  blast  are  being  obtained  which 
are  not  exceeded  anywhere  by  the  hot  blast. 

According  to  recent  reports,  Mr.  Johnson  is  now  put- 
ting in  hot  blast  in  a  new  smelter  he  is  erecting  on  the 
northwest  coast,  where  the  conditions  are  somewhat 
different  from  those  where  he  formerly  operated  in 
British  Columbia. 

Mr.  J.  W.  Nesmith  gives  the  results  of  a  test  run 
made  at  Silverton,  Colo.,  at  the  matte  smelter  formerly 
owned  by  Thomas  F.  Walsh,  the  metallurgist  in  charge 
being  E.  W.  Walter. 

70 


L.  D.  GODSHALL. 
The  following  are  the  results : 

Cold  blast.  Hot  blast,  700°  F. 

90  hours.     Duration  of  test 72  hours. 

104  tons . .    Charges   per   24   hours 150  tons. 

300  Ib Coke    used    per    charge 150  lb. 

7  into  1    Degree  of  concentration 7  into  1. 

$109.20.  ...     Cost  of  coke $78.75 

Cost  of  heating  hot  blast 34.50 

— $113.25 

The  above  figures  are  of  great  value  as  illustrating 
three  important  points :  Capacity,  fuel  required  in  fur- 
nace, and  oxidation  of  sulphur.  The  smelting  capacity 
is  so  clearly  in  favor  of  the  hot  blast  for  this  particular 
charge  that  the  inference  naturally  follows  that  there 
may  be  many  other  cases  where  such  capacity  must  be 
equally  favored  by  the  aid  of  it,  but  it  does  not  neces- 
sarily follow  that  all  ores  will  show  such  a  variation  be- 
tween hot-  and  cold-blast  smelting. 

Economy  in  fuel  is  as  important  a  factor  as  capacity 
in  smelting.  The  saving  in  coke  brought  about  by  the 
external  heating  of  the  blast  must  exceed  the  actual  ex- 
pense cf  such  external  heating  in  order  to  become  an 
economical  advantage.  Some  writers  speak  of  such 
saving  of  coke  as  self-evident,  but  it  must  be  remem- 
bered that  in  heating  the  blast  inside  of  the  furnace  by 
means  of  coke  alone,  all  of  the  heat  contained  in  the 
latter  is  utilized.  In  the  case  of  the  external  applica- 
tion of  heat  to  the  blast,  cheaper  fuel  is  available ;  but, 
on  the  other  hand,  heavy  losses  in  heat  occur  by  radia- 
tion and  otherwise. 

Where  fuel  cheap  in  comparison  with  coke  can  be 
obtained,  and  the  mechanical  appliances  are  so  per- 
fected as  to  utilize  the  greatest  possible  amount  of  heat 
contained  in  such  fuel,  there  ought  to  be  no  question  of 
the  economy  of  the  hot  blast  so  far  as  the  fuel  question 
is  concerned.  On  the  other  hand,  where  the  difference 
between  the  cost  of  coke  and  other  fuels  is  not  so 
marked,  the  economy,  in  fuel,  of  the  externally  heated 

71 


PYRITE  SMELTING. 

blast  is  very  materially  lessened,  and  may  in  some  cases 
become  doubtful. 

The  experience  at  the  Silverton  smelter,  as  shown  by 
the  above  data,  leaves  no  doubt  in  that  case  as  to  the 
economy  of  the  hot  blast.  In  that  test,  using-  cold  blast, 
390  charges  were  smelted  at  a  total  cost  for  fuel  of 
$109.20,  while  with  the  hot  blast,  450  charges  were 
smelted  at  a  cost  of  $113.25.  The  weight  of  the 
charge  is  not  given,  but,  judging  from  the  weight  of 
charges  given  in  connection  with  other  data,  it  prob- 
ably was  from  2,000  to  2,500  Ib.  It  will  therefore  be 
readily  seen  that  in  this  case  the  total  fuel  required  for 
the  hot-blast  test  cost  but  $4  more  than  that  for  the 
cold  blast,  and  for  this  extra  expenditure  of  $4  more 
than  60  tons  of  additional  charge  were  smelted.  The 
importance  of  the  proved  advantage  of  the  hot  blast  in 
some  instances  should  make  the  subject  of  sufficient  in- 
terest to  all  metallurgists  to  give  it  their  most  careful 
consideration  and  study ;  for  that  which  to-day  is  a  suc- 
cess, under  certain  limited  conditions,  may  to-morrow 
be  improved  and  its  use  widely  extended. 

The  consumption  of  coke  in  hot-  or  cold-blast  smelt- 
ing varies  according  to  the  amount  of  sulphur  present  in 
the  charge.  The  following  figures  are  given  as  repre- 
senting the  approximate  percentages  used  under  dif- 
ferent conditions: 

Per  cent. 

Mt.  Lyell,  with  hot  blast  and  double  smelting;  coke  used 
per  ton  ore  smelted 6 

Bingham,  Utah,  with  cold  blast  and  double  smelting;  es- 
timated coke  consumption  on  ore  smelted 10 

Butte,   Mont.,   single  smelting,    with   cold   blast 10  to  11 

British  Columbia,  single  smelting,  with  cold  blast  and 
raw  ore  low  in  copper  and  sulphur 12  to  13 

In  all  of  the  above  cases,  the  grade  of  the  matte  is 
estimated  to  be  on  a  basis  of  45  to  50  per  cent  copper, 
and  the  percentage  of  coke  is  based  on  ore  smelted. 

In  an  article  entitled  'Smelting  at  Mt.  Lyell,  Tasma- 
nia/ Mr.  Alfred  Miller  makes  the  statement  that  coke 

72 


L.  D.  GODSHALL. 

had  recently  been  entirely  eliminated  in  the  raw  ore 
smelting  at  Mt.  Lyell,  and  in  addition  to  the  above  inno- 
vation the  hot  blast,  which  had  been  found  in  pre- 
vious experience  to  be  "obligatory  and  not  to  be  cir- 
cumvented," had  been  lowered  in  temperature,  and  that 
in  No.  i  plant  both  ore  and  matte  were  now  being 
smelted  with  cold  blast.  This  marks  such  a  change 
and  improvement  over  past  experience  that  additional 
information  on  the  subject  would  prove  of  very  great 
interest. 

The  relative  economy  of  the  different  methods  of 
matte  smelting  at  present  in  use  is  a  most  difficult  ques- 
tion to  determine. 

The  competing  methods  adapted  to  the  smelting  of 
sulphide  ores  carrying  a  small  percentage  of  copper  are 
as  follows : 

1.  The  hot  blast,  double-smelting  process  for  raw 
ores. 

2.  The  cold  blast,  double-smelting  process  for  raw 
ores. 

3.  The  cold  blast,  single-smelting  process,  requiring 
a  preliminary  roasting  of  all  or  part  of  the  heavy  sul- 
phide ore  treated. 

4.  The  reverberatory  process,  requiring  a  preliminary 
roasting. 

According  to  some  of  the  literature  on  pyritic  smelt- 
ing there  is  only  one  way  to  smelt  heavy  pyritic  ores, 
and  the  expense  of  that  method  is  so  extremely  low  that 
no  other  method  can  possibly  compare  with  it.  To  show 
the  fallacy  of  such  claims  without  further  argument  it  is 
merely  necessary  to  point  to  two  notable  instances :  The 
Highland  Boy  smelter  at  Salt  Lake,  treating  heavy  py- 
ritic ore,  containing  a  low  percentage  of  copper  and  very 
small  quantities  of  gold  and  silver ;  and  the  Argo  smel- 
ter at  Denver,  treating  heavy  pyritic  ores  and  concen- 
trates low  in  copper,  but  frequently  high  in  gold  and 
silver.  The  fact  that  the  latter  stands  to-day  as  the  re- 

73 


PYRITE  SMELTING. 

suit  of  development,  from  the  old  Welsh  process  which 
was  crude  and  primitive  when  first  introduced  into  this 
country  by  Mr.  Richard  Pearce,  while  the  former  is  a 
modern  reverberatory  furnace  plant  erected  but  a  few 
years  and  designed  by  a  noted  copper  metallurgist,  de- 
notes that  reverberatory  practice  is  still  a  healthy  rival 
of  the  blast  furnace  methods. 

The  long-continued  success  of  both  also  gives  weight 
to  the  argument.  The  important  discoveries  and  devel- 
opments made  in  connection  with,  and  bearing  upon,  the 
different  methods  of  matte  smelting  may  be  summed 
up  as  follows : 

1.  Direct  smelting  of  heavy  raw  sulphide  ores,  with 
either  hot  or  cold  blast,   and     oxidizing    a     sufficient 
amount  of  sulphur  to  provide  the  necessary  iron  oxide 
for  fluxing  purposes. 

2.  Concentration  of  copper  in  matte  so  produced,  by 
a  second  direct  smelting  to  approximately  50  per  cent 
copper,    thereby   rendering  it  suitable    for    converting 
without  any  previous  roasting. 

3.  Important  improvements    and     developments    in 
mechanical  roasting  furnaces,  whereby  the  cost  of  roast- 
ing has  been  greatly  reduced,  thereby  lessening  the  cost 
of  copper  smelting  and  matte  smelting  as  distinguished 
from  pyritic  smelting. 

4.  Important  improvements    and    developments    in 
water  concentration,  greatly  reducing  the  losses  former- 
ly sustained,  thereby  lessening  the  advantages  of  direct 
smelting  of  the  crude  ore. 

5.  The  successful  application  of  the  hot  blast  with  its 
decreased  amount  of  coke  required  for  smelting. 

It  is  not  likely  that  the  accuracy  of  the  above  state- 
ments will  be  questioned  by  any  of  the  metallurgists, 
however  widely  they  may  differ  on  many  other  points. 
The  first  four  statements  are  self-evident ;  the  fifth,  with- 
out any  further  explanation,  might  be  objected  to  as  not 
stating  the  whole  proposition,  because  it  sets  aside,  for 

74 


L.  D.  GODSHALL. 

the  moment,  the  question  of  the  relative  economy  of 
hot,  as  against  cold,  blast.  Those  who  deny  the  econ- 
omy of  the  hot  blast  are,  however,  forced  to  admit  that 
it  is  practical.  For  this  reason  the  question  of  economy 
is  omitted  from  the  statement. 

In  determining  the  question  of  the  relative  economy 
of  the  different  methods,  it  is  always  necessary  to  take 
into  consideration  the  character  of  the  ore,  both  chem- 
ical and  physical,  the  cost  of  supplies  and  the  cost  and 
character  of  fuel  and  labor. 

Some  of  the  writers  on  this  subject  make  a  great 
point  of  the  advantage  of  direct  smelting  without  roast- 
ing, but  neglect  to  take  into  consideration  the  cost  and 
disadvantage  of  a  second  smelting  of  the  first  matte  pro- 
duced. They  also  overlook  the  improvements  recently 
made  in  modern  mechanical  roasting  furnaces,  whereby 
the  heat  from  the  burning  sulphur  is  utilized  and  fuel 
almost  eliminated,  reducing  the  cost  of  roasting  to  a 
minimum.  In  many  instances  there  are  very  distinct 
advantages  to  be  derived  in  the  single  smelting  preceded 
by  the  roasting  of  heavy  sulphide  ores.  Where  copper 
ores  are  scarce,  but  necessary  for  making  clean  slag,  a 
preliminary  roasting  will  produce  a  much  higher  con- 
centration and  therefore  higher  grade  copper  matte, 
which  means  a  correspondingly  smaller  amount  of  cop- 
per on  the  charge.  Where  copper  ores  are  brought 
from  a  distance  and  smelted  at  a  loss  merely  for  the 
sake  of  the  copper,  to  produce  clean  slags,  such  differ- 
ence might  change  failure  into  success.  Where  appre- 
ciable quantities  of  zinc  sulphide  accompany  the  ore  a 
preliminary  roasting  will  be  of  the  very  highest  impor- 
tance, as  pointed  out  by  Mr.  Ingalls.  Zinc-blende  is 
one  of  the  most  difficult  minerals  to  oxidize,  and  if  put 
in  the  furnace  raw,  in  large  quantities,  it  will  check  the 
smelting  capacity,  form  crusts  of  sublimated  zinc  sul- 
phide along  the  furnace  walls  and  derange  the  operation 
of  the  furnace  generally.  Some  will  be  oxidized  and  en- 

75 


PYRITE  SMELTING. 

ter  the  slag  as  ZnO,  and  the  balance  will  be  found  dis- 
tributed partly  in  the  slag  and  partly  in  the  matte,  in 
both  cases  in  a  dissolved  state,  and  still  another  portion 
will  be  found  floating  away  in  the  slag  like  mushy  ice  or 
snow  in  water.  Under  such  conditions  clean  slags  are 
next  to  impossible  to  obtain,  while  with  a  preliminary 
roasting  most  of  the  zinc  will  enter  the  slag  as  ZnO, 
producing  cleaner  slags  and  avoiding  the  mechanical 
troubles  of  the  blast  furnace.  In  addition,  high  zinc 
slags  invariably  require  a  heavy  percentage  of  iron,  and 
render  therefore  the  usually  profitable  and  always  de- 
sirable high  silica  slags  an  impossibility. 

Messrs.  Carpenter  and  Lang  both  advocate  the  di- 
rect smelting,  without  concentration,  of  Butte  ores,  but 
if  we  take  into  consideration  that  these  ores  by  analysis 
show  the  following  composition :  SiO2,  58  per  cent ;  Fe, 
12  per  cent ;  S,  17  per  cent ;  Cu,  4  per  cent,  it  becomes 
apparent  at  once  that  such  smelting  would  be  exceed- 
ingly costly  by  reason  of  the  excessive  amount  of  fluxes 
and  fuel  required,  and  it  seems  to  the  writer  that  it 
would  be  better  to  first  demonstrate  the  advantage,  if 
there  be  any,  of  smelting  the  present  Butte  charge  raw 
or  without  any  previous  roasting.  If  it  cannot  be  dem- 
onstrated that  the  low  silica  and  high  sulphur,  under 
such  conditions,  can  be  smelted  more  advantageously 
raw  than  it  is  now  being  done,  it  would  seem  to  be  still 
more  difficult  to  demonstrate  the  advantage  of  smelt- 
ing, raw,  the  low-grade  mill  ore,  which  is  much  higher 
in  silica  and  correspondingly  lower  in  sulphur. 

In  conclusion  the  writer  wishes  to  suggest  that  there 
is  one  field  not  yet  entered  by  matte  smelting  which,  in 
his  opinion,  deserves  attention ;  that  of  smelting  dry 
ores  by  matte  smelting  as  against  lead  smelting,  in  cen- 
tral localities  like  Denver  and  Pueblo  in  Colorado,  and 
the  Salt  Lake  valley  in  Utah.  Matte  smelting  under 
such  conditions  should  be  carried  on  by  one  smelting  to 
produce  45  to  50  per  cent  copper  matte,  and  all  heavy 

76 


L.  D.  GODSHALL. 

sulphide  ores  should  be  roasted.  Under  such  conditions 
we  would  have  the  following  advantages  as  compared 
with  lead  smelting1: 

Slags  comparatively  as  clean  as  in  lead  smelting. 

High,  instead  of  low,  silica  slags. 

Capacity  of  matte  furnace  nearly  twice  that  of  lead 
furnace. 

Result,  very  much  lower  cost  per  ton  of  ore  smelted. 

L.  D.  GODSHALL. 
Denver,  Colo.,  Dec.  20,  1903. 


77 


CONTRIBUTION  BY  WILLIAM  A.  HEYWOOD. 

The  Editor : 

Sir — As  a  contribution  to  the  discussion  on  raw  sul- 
phide smelting,  I  give  the  results  of  a  series  of  experi- 
ments recently  made  at  the  plant  of  the  Tennessee  Cop- 
per Company,  using  cold  blast.  The  ore  treated  is  a 
pyrrhotite  mixed  with  schist  containing  approximately 
2.5  per  cent  Cu,  40  per  cent  Fe,  25  per  cent  S,  and  25 
per  cent  insoluble.  The  furnace  used  was  ^6  by  180  in. 
at  the  tuyeres  and  72  by  180  in.  at  the  top,  water  jack- 
ets 15  ft.  high.  Air  was  blown  through  28  tuyeres  of  4 
in.  diameter.  For  supplying  the  blast  a  Nordberg 
cross-compound  blowing  engine  was  used,  and  the 
quantity  of  air  consumed  in  each  experiment  was  care- 
fully noted.  The  experiments  were  made  to  determine 
the  results  of  different  volumes  of  air.  Only  the  air 
factor  was  changed  in  each  experiment ;  probably  by 
varying  other  factors  more  favorable  results,  especially 
a  higher  rate  of  concentration,  may  be  obtained  : 


Tons  ore  smelted  per 
day    

No.  1. 
401 

No.  2. 

228 

No.  3. 
267 

No.  4. 
276 

No.  5. 

468 

Tons    quartz     smelted 

50 

19 

22 

23 

39 

Tons    other     material 
per  day 

74 

Total  charge  per  day. 
Tons    coke    used    per 
day   

525 
56 

247 

5  7 

289 
67 

299 

69 

507 
11  7 

Per     cent      coke     on 
charge 

103 

23 

23 

23 

23 

Per  cent    coke  on  ore 
smelted 

139 

25 

25 

25 

2  5 

Per    cent      copper    in 
matte  made 

400 

7.7 

11.0 

8.4 

81 

Per    cent     copper    in 
slag  made 

043 

014 

0.11 

012 

0  11 

Per  cent  insol.  in  slag 
Per  cent    FeO  in  slag. 
Cubic     feet     free     air 
per  minute    

32.0 
51.0 

16800 

41.0 
37.2 

14,400 

39.2 
40.6 

16,800 

390 
40.0 

19200 

390 
41.0 

22080 

Height     of     charge 
above  tuyeres    .... 

lift. 

6.5  ft. 
78 

6.5  ft. 

6.5  ft. 

6.5  ft. 

WILLIAM  A.  HEYWOOD. 

No.  i  is  an  average  daily  run,  calculated  from  six 
months'  smelting  of  heap-roasted  ore  with  quartz,  con- 
verter slag  and  some  custom  matte.  No.  2,  3,  4  and  5 
are  the  experimental  runs  on  raw  sulphides  with  quartz 
and  2.5  per  cent  coke.  With  the  exception  o(  the  blast, 
all  the  conditions  were  kept  as  nearly  the  same  as  possi- 
ble. The  quantity  of  ore  smelted  seems  to  be  in  propor- 
tion to  amount  of  air  blown  into  the  furnace.  In  these 
experiments  the  rate  of  concentration  appears  to  bear 
no  relation  to  the  rate  of  smelting. 

The  low-grade  matte  made  in  these  experiments  was 
re-smelted  with  converter  slag,  quartz  and  6  per  cent 
coke  on  the  charge,  producing  a  40  per  cent  copper 
matte,  which  was  converted,  and  a  slag  containing  28.4 
per  cent  insoluble,  54  per  cent  FeO,  and  0.46  per  cent 
copper. 

The  furnace  ran  smoothly  throughout  the  experi- 
ments. No  difficulty  or  delay  was  experienced  in  chang- 
ing from  the  usual  roasted  ore  charge  to  raw  ore  or 
vice  versa.  During  experiment  No.  5  the  slag  and  matte 
were  so  extremely  hot  that  it  was  apparent  that  the  coke 
could  be  either  materially  reduced  or  entirely  elim- 
inated. 

A  great  deal  has  been  written  on  the  subject  of  hot 
blast,  but  I  have  never  found  any  definite  comparison 
published  on  the  treatment  of  any  particular  sulphides 
or  class  of  ores  by  both  hot  and  cold  blast.  I  am  sure 
it  would  be  of  great  interest  if  some  metallurgist  would 
give  the  comparative  results,  both  metallurgical  and 
financial,  of  both  methods  of  smelting;  in  other  words, 
to  add  to  the  volumes  that  have  been  written  on  what 
may  be  done  with  hot  blast,  a  few  words  on  what  has  been 
done.  WILLIAM  A.  HEYWOOD. 

Copperhill,  Tenn.,  Jan  29,  1904. 

Since  the  above  was  written  the  experiments  have 
been  continued.  Matte  containing  12  to  16  per  cent  Cu 

79 


PYRITE    SMELTING. 

has  been  produced  in  our  later  campaigns  with  a  slag 
containing  40  per  cent  insol.,  40  per  cent  FeO  and  0.15 
per  cent  Cu.  The  mattes  produced  show  an  excess  of 
Fe  amounting  to  n  to  13  per  cent  over  the  Fe  required 
for  the  formula  Cu2S,  FeS.  This  iron  is  present  as  an 
oxide ;  both  chemical  and  microscopic  examinations  of 
the  matte  showed  no  metallic  iron. 

WILLIAM  A.  HEYWOOD. 
July  28,  1904. 


80 


CONTRIBUTION  BY  G.  F.  BEARDSLEY. 

The  Editor : 

Sir — 'Raw  sulphide'  smelting,  'matte'  smelting,  'py- 
ritic'  smelting;  I  have  no  wish  to  quarrel  with  terms, 
any  of  which  are  not  exactly  descriptive  of  the  fusion 
of  iron-  or  copper-bearing  sulphides  by  their  rapid  oxi- 
dation in  the  blast-furnace  under  suitable  con- 
ditions ;  that  is,  hot  blast  and  small  quantities  of 
coke.  To  the  term  pyritic  smelting,  however,  the  above 
definition  has  become  attached,  and,  I  am  afraid,  cannot 
be  shifted.  I  will  use  it  as  indicated  above.  To  save 
repetition  I  will  also  use  iron  'sulphide  minerals'  as  in- 
cluding pyrite,  pyrrhotite  and*  chalcopyrite,  and  'pyrite' 
or  'pure  pyrite'  as  a  pyritic  ore  containing  90  per  cent 
FeS2  +  nCuFeS2,  with  10  per  cent  of  impurities,  con- 
sisting of  silica  3  to  5  per  cent,  barite  I  to  2  per  cent, 
alumina  2  to  3  per  cent,  other  constituents  0.5  to  1.5 
per  cent. 

i.  What  types  of  ores  are  suited  to  the  process? 

Pure  pyrite  and  pure  pyrrhotite,  pre-eminently.  The 
furnace  charge  at  Mount  Lyell  averaged  21  per  cent  sil- 
ica, 30  per  cent  iron,  35  per  cent  sulphur,  and  10  per 
cent  of  earthy  bases,  including  about  5  per  cent  alumina. 
This  may  be  taken  as  a  type,  and  any  composition  of  ore 
between  this  and  pure  pyrite  can  be  smelted  with  3  per 
cent  of  coke  or  less,  provided  the  physical  condition  of 
the  ore  is  not  against  it,  that  is,  fine  ore,  large  lumps 
of  pure  silica,  or  pure  schist,  or  an  even  blending  of  the 
above  constituents  in  the  pieces  of  ore.  It  is  necessary 
that  a  certain  proportion  of  the  ore  be  of  sufficient  pur- 
ity to  start  running  as  a  matte  at  a  comparatively  low 
heat  in  the  upper  part  of  the  charge.  This  filtering 
through  the  coarse  material,  oxidizing  with  the  ascend- 

81 


PYRITE    SMELTING. 

ing  blast,  generates  heat,  at  the  same  time  dissolving 
and  fluxing  the  more  infusible  portions  of  the  charge. 
An  even  blending  of  20  per  cent  silica  plus  10  per  cent  of 
bases,  and  equal  to  about  one-third  of  the  bulk  or  weight 
of  the  ore-lumps,  will  seriously  retard  this  effect. 

2.  Is  hot  blast  advisable  ? 

I  think  it  advisable,  and  in  some  cases  necessary. 
It  is  advisable  when  the  blast  can  be  heated  by  waste 
gases.  It  is  necessary  where  it  is  desirable  to  force  as 
much  silica  into  the  slag  as  possible.  At  Mount  Lyell, 
as  the  charge  column  was  gradually  raised  and  the  blast 
increased,  the  stove-heat  was  taken  off,  until  finally 
stoves  were  not  used  at  all.  Hot-blast  pipe-stoves  are 
certainly  a  most  wasteful  apparatus  for  heating  air. 
From  300°  to  500°  F.  should  be  picked  up  from  the 
waste-gases  of  the  furnace  with  a  proper  arrangement, 
especially  if  there  is  sufficient  volatilized  sulphur  to  burn 
above  the  surface  of  the  furnace  charge. 

3.  To  what  extent  can  fuel  be  eliminated '? 

This  depends  upon  two  conditions :  the  quantity  of 
iron  sulphide  minerals  in  the  ore,  which  are  the  heat 
producers,  and  the  relation  of  those  minerals  to  the 
gangue.  To  go  back  to  the  approximate  furnace-charge 
analysis  under  the  first  question :  with  a  mixture  of  py- 
rite  and  a  silicious  aluminous  schist  containing  5  per 
cent  iron,  and  4  to  8  per  cent  copper  in  the  form  of  bor- 
nite,  but  with  the  sulphide  mineral  in  concentrated  and 
isolated  patches  in  the  gangne,  2.5  to  3  per  cent  of  coke 
was  required,  and  the  campaigns  were  short.  With  the 
same  approximate  analysis,  but  with  a  laminated  schist 
containing  8  per  cent  of  iron  and  1.5  per  cent  of  cop- 
per, with  the  sulphide  mineral  scattered  somewhat  even- 
ly through  it  in  small  grains,  practically  the  same  fur- 
nace-charge is  smelted  with  0.3  to  0.4  per  cent  of  coke, 
and  the  campaigns  last  from  60  to  80  days.  There  is  no 
ore,  carrying  an  appreciable  quantity  of  iron  sulphide 

82 


G.  F.  BEARDSLEY. 

minerals,  upon  which  some  pyritic  effect  cannot  be  ob- 
tained in  the  way  of  reduction  of  fuel  in  the  smelting. 

4.  What  amount  of  copper  is  needed  for  the  collection  of 
the  precious  metals  ? 

I  note  that  some  metallurgists  maintain  that  cop- 
per is  not  an  absolute  necessity,  and  that  clean  slags 
can  be  made  with  iron  matte  alone.  My  own  experi- 
ences in  pyritic  smelting  have  been  limited  to  1.5  per 
cent  and  over  of  copper  in  the  charge ;  with  the  lowest 
copper  I  have  always  had  clean  slags. 

5.  What  percentage  of  lime  is  necessary  to  a  clean  slag? 
The  copper  matte  is  the  slag  cleaner,  not  the  lime. 

Enough  lime  or  bases,  including  alumina,  to  make  the 
most  liquid  slag  obtainable,  is  all  that  is  required.  This 
allows  the  free  settling  of  the  matte  particles.  With 
alumina  and  barite  present,  I  usually  aim  at  a  quarter 
slag  containing  about  13  per  cent  of  bases  other  than 
iron,  and  vary  the  lime  to  suit  that  requirement.  One- 
fifth  slags  work  well  also ;  but,  going  below  that,  the  de- 
ficiency of  the  lighter  bases  raises  the  specific  gravity  of 
the  slag,  and  is  liable  to  cause  a  poorer  settlement  of  the 
fine  shots  of  matte. 

6.  What  percentage  of  zinc  in  the  charge  can  be  treated 
profitably  ? 

I  have  had  no  special  experience ;  but  very  small 
amounts  in  the  ores  I  have  been  treating.  I  have  no- 
ticed, however,  on  one  or  two  occasions,  in  the  side 
accretions,  more  particularly  in  the  furnace  corners, 
small  quantities  of  the  zinc-lead  sulphide  which  usually 
forms  the  collar  accretions  in  lead  furnaces.  If  there 
were  no  lead  in  a  pyritic  ore  it  is  possible  that  some  zinc 
might  be  carried  through,  but  I  believe  it  would  give 
trouble  in  the  forehearth. 

7.  What  is  the  degree  of  de  sulphur  ization  attainable? 

I  have  been  in  the  habit  of  figuring  on  the  oxidation 
attainable ;  one  is  the  converse  of  the  other  to  a  great 

83 


PYRITE    SMELTING. 

extent.  The  degree  of  oxidation  determines  the  matte- 
fall.  The  higher  the  oxidation,  the  smaller  the  matte- 
fall  and  the  higher  the  grade  of  the  matte.  Oxidizing 
80  per  cent  of  the  Fe  present  in  90  per  cent  pyrite, 
which  is  high  in  practice,  will  give  a  desulphurization 
of  90  per  cent,  and  oxidizing  60  per  cent  of  the  iron, 
which  is  low,  will  give  an  80  per  cent  desulphurization. 

8.  What  are  the  possibilities  as  to  capacity  of  furnace? 
The  table  below  gives  some  dimensions  of  furnaces : 

2,000  Ib.  tons  of  charge  per 

Area  of  , 24  hours. >  Tons  per  sq.  ft.  of  hearth 

Size  of       Hearth       Blast  20  to         Blast  40  to  , area. . 

Furnace,    in  sq.  ft.         80  oz.  45  oz.  25  to  80  oz.    40  to  45  oz. 

126  by  36      31.50  199.08  tons       284.57  tons  6.31  tons       9.03  tons. 

168  by  40      46.16  217.43     "  402.94    "  4.65     "  8.60    " 

210  by  42      61.25  271.43     ••  530.76    ••  4.42     "  8.65    " 

On  a  pure  pyritic  ore,  under  the  most  favorable  cir- 
cumstances and  with  50  oz.  of  blast,  I  have  no  doubt 
that  the  quantities  could  still  be  increased  by  a  fifth. 
The  larger  furnaces  give  a  smaller  hearth-efficiency,  but 
the  labor-efficiency  is  largely  increased,  that  is,  the  num- 
ber of  men  to  run  the  furnace  is  not  increased  in  pro- 
portion to  the  additional  tonnage  treated  per  day. 

9.  What  are  the  limitations  of  the  process  ? 

The  answer  to  this  may  be  deduced  from  the  answer 
to  question  No.  3.  It  is  an  oxidation  process,  and  nat- 
urally shades  off  from  pure  pyritic  ore,  where  the  oxida- 
tion must  be  the  highest,  to  those  oxidized  ores  that  do 
not  require  it  at  all ;  from  those  ores  of  sufficient  fuel- 
value  to  furnish  their  own  heat  for  fusion,  through 
those  that  must  be  assisted  by  varying  quantities  of  ex- 
traneous fuel,  to  those  that  have  to  be  smelted  entirely 
by  it  It  also  may  be  limited  by  excessive  quantities  of 
zinc  and  lead. 

10.  What  is  the  relative  economy  as  compared  to  rival 
processes ? 

It  has  no  rival,  where  suitable.  As  against  the  kiln  or 
heap-roasting,  previous  to  blast-smelting,  there  is  a 
large  saving  in  the  expensive  fuel,  coke;  a  complete 

84 


G.  F.  BEARDS  LEY. 

elimination  of  the  cheaper  fuel  used  for  starting  the 
roast-heaps,  namely,  wood;  a  saving  in  the  labor  ot 
handling  the  ore  to  and  from  the  roast-yard;  a  saving 
in  the  interest  on  a  large  quantity  of  dead  stock  locked 
up  in  the  roast-heaps,  and  a  great  saving  in  the  loss  of 
copper  by  leaching,  especially  in  wet  countries.  With 
8  to  12  ft.  of  rain  per  year,  as  is  the  case  on  the  west 
coast  of  Tasmania,  open  roast-heaps  are  simply  out  of 
the  question.  To  cover  the  heaps  required  to  furnish 
l,ooo  tons  of  ore  per  day  would  mean  a  heavy  first  cost 
and  a  heavy  maintenance  cost. 

One  of  the  most  striking  advantages  is  the  rapidity  of 
the  work.  Eliminating  the  periods  for  cooling  the  matte 
between  the  several  operations,  the  actual  time  from 
the  feeding  of  the  ore  into  the  furnace  to  the  pouring 
of  the  blister  copper  into  the  moulds  from  the  converter 
vessels  is  about  5.5  hours.  This  includes  the  smelting 
of  the  ore  and  the  production  of  a  first  matte  of  9  to  15 
per  cent  copper,  the  resmelting  of  the  first  matte,  pro- 
ducing converter  matte  of  40  to  50  per  cent  copper,  and, 
finally,  the  melting  and  blowing  the  converter  matte 
to  blister  copper.  If  converter  matte  is  made  direct 
from  mixed  ores,  then  the  time  of  treatment  is  but  3.5 
hours.  I  might  here  add  a  note  that  so  far  as  the  fur- 
nace manipulation  is  concerned,  pyritic  smelting  is  the 
most  delicate  of  all  blast-furnace  work.  With  little  or 
no  coke  in  the  furnace  there  is  no  latitude  for  any  appli- 
cation of  the  remedies  common  to  other  work,  and  al- 
though, when  absolutely  necessary,  a  sudden  shut-down 
of  an  hour  may  be  made,  it  will  take  seven  or  eight 
hours  to  recover  from  it,  and  often  the  foundation  is  laid 
for  a  trouble  that  does  not  manifest  itself  for  a  day  or 
two.  Short  campaigns  are  the  rule,  and  the  frequent 
shutting  down  of  a  furnace  must  be  considered  as  part 
of  the  process. 

G.  F.  BEARDSLEY. 
San  Francisco,  Jan.  9,  1904. 

85 


CONTRIBUTION  BY  THOMAS  T.  READ. 

The  Editor : 

Sir — A  good  example  of  the  smelting  of  raw  sulphides 
of  iron  and  copper,  utilizing  the  heat  of  combustion  of 
the  sulphur  content  to  replace  a  portion  of  the  coke 
usually  required,  is  seen  at  the  plant  of  the  United 
States  Smelting  Company  at  Bingham  Junction,  about 
15  miles  from  Salt  Lake  City,  Utah. 

This  plant  is  at  present  smelting  about  700  tons  daily, 
but  the  work  of  enlarging  it  to  1,000  tons  capacity  is 
already  under  way.  The  larger  part  of  this  tonnage  is 
derived  from  the  company's  mines  at  Bingham  canon, 
but  ores  from  the  Boston  Consolidated  are  also  being 
smelted.  The  ore  is  of  two  classes,  a  silicious  ore  that 
presents  no  especial  difficulties,  and  a  sulphide  ore  that 
breaks  up  into  fine  particles  and  gives  rise  to  the  diffi- 
culties which  are  always  met  in  the  smelting  of  fine  ore. 
The  average  content  of  the  two  ores  is  about  2  per  cent 
copper  and  nearly  equal  values  of  gold  and  silver. 

The  plant  has  only  been  in  operation  about  a  year  and 
is  essentially  modern  and  up  to  date  in  every  particular. 
Being  situated  on  the  eastern  side  of  the  valley  of  the 
river  Jordan  it  has  the  sloping  site  necessary  for  the 
ellipsoidal  arrangement  of  track  and  ore-bins  which 
characterizes  the  late  designs  of  smelting  plants.  The 
smelter  and  converter  houses,  or  house,  for  they  are  un- 
der one  roof,  are  of  structural  steel  and  sheet  iron ;  the 
power-house  is  of  brick  and  the  ore-bins  are  of  the 
usual  timber  construction. 

The  ore  is  delivered  at  the  smelter  from  the  mines  in 
5O-ton  cars  and  goes  first  xo  the  sampling  bin  and  then 

86 


THOMAS  T.  READ. 

to  the  storage  bins.  These  are  provided  with  hopper 
bottoms  and  Fairbanks  track-scales  beneath.  These 
scales  are  set  at  the  desired  weights  in  the  usual  way 
and  the  charging  cars,  drawn  in  a  train  by  an  electric 
locomotive,  are  weighed  directly  as  they  are  being  filled. 
From  the  bins  the  trains  go  to  the  charging  floor,  where 
the  cars  are  dumped  on  a  shoveling-plate.  As  designed, 
it  was  intended  to  charge  the  furnaces  directly  from  the 
cars,  but  this  was  found  unsatisfactory  and  charging  by 
shovel  was  substituted.  A  slight  change  has  been  made 
in  the  design  of  one  of  the  furnaces  and  automatic 
charging  is  to  be  again  tried. 

The  furnaces  are  five  in  number  (four  in  blast),  42  in. 
by  180  in.,  water-jacketed  with  round  brick  settlers. 
Apparently  the  width  is  a  little  too  great  under  the  cir- 
cumstances— that  is,  with  a  charge  containing  a  good 
deal  of  fine  and  a  highly  silicious  slag — for  it  renders 
necessary  a  high  blast  pressure  (30  oz.),  to  secure  pene- 
tration which,  in  conjunction  with  the  finely  divided 
condition  of  the  ore,  makes  an  excessive  quantity  of 
flue-dust,  so  much  indeed  that  it  is  difficult  to  handle. 
Having  to  put  all  this  back  through  the  furnaces,  after 
briquetting,  tends  to  increase  the  trouble.  Apparently 
narrower  furnaces  with  larger  tuyeres  and  a  lower  blast 
pressure  would  give  better  satisfaction.  With  such  a 
high  blast-pressure  the  end  tuyeres  on  the  sides  would 
cause  a  chill  if  allowed  to  remain  open,  and  are  there- 
fore kept  plugged. 

The  heat  of  combustion  of  the  sulphur  allows  the 
coke  to  be  cut  to  6  or  7  per  cent.  A  hot  blast  has  been 
used  on  two  of  the  furnaces  with  apparent  success,  but 
the  hot-blast  stove  has  required  closing  down  for  re- 
pairs so  often  that  no  results  that  are  really  conclusive 
have  as  yet  been  obtained.  No  attempt  is  made  to  util- 
ize the  heat  of  the  flue-gases.  The  flue  is  constructed 
of  brick,  with  sheet  steel  downtakes.  These  latter  were 
at  first  made  of  6  ft.  diameter,  but,  being  the  cause  of  a 

87 


PYRITE  SMELTING. 

very  gassy  charging  floor,  were  replaced  by  others  7  ft. 
in  diameter  with  a  marked  improvement. 

The  first  matte  from  three  of  the  furnaces  averages 
about  15  per  cent  copper  and  is  cast  in  the  usual  way. 
It  then  goes  back  to  the  fourth  furnace,  together  with  a 
nearly  equal  percentage  of  ore.  The  matte  from  this 
furnace  runs  from  25  to  30  per  cent  copper  and  goes 
directly  to  the  converters,  where  it  is  blown  up  to  blister 
copper.  This  is  then  cast  into  pigs  and  shipped  to  an 
eastern  refinery.  The  casting  of  anode  plates  is  not  at- 
tempted at  any  plant  in  the  district. 

A  large  economy  in  the  handling  of  the  slag  is  ef- 
fected by  granulating  it.  The  granulated  slag  is  led  into 
two  settling  tanks,  alternating  from  one  to  the  other, 
so  that  while  the  slag  is  being  removed  from  one  tank 
the  other  is  filling.  These  tanks  are  fitted  with  hopper 
bottoms,  so  that  the  slag  larry  can  be  brought  beneath 
and  filled  directly.  The  slag  is  then  trammed  to  the 
southern  end  of  the  property  and  dumped.  There  is 
sufficient  fall  to  allow  of  wasting  the  slag  directly 
from  the  end  of  the  flume,  but  the  fear  of  allowing  it  to 
enter  the  Jordan  river  has  so  far  prevented  this.  The 
water  for  the  granulation  of  the  slag  and  the  general 
supply  of  the  plant  is  obtained  from  a  ditch  taken  out 
of  the  river  some  distance  up-stream.  As  the  formation 
of  anchor  ice  in  winter  and  irrigation  in  summer  are 
likely  to  diminish  this  supply,  a  pumping  system  has 
been  installed,  which  is  capable  of  supplying  the  entire 
plant  from  the  Jordan  river  directly  opposite  the  plant. 
In  addition  there  are  three  artesian  wells  which  are 
pumped  by  the  Poehle  system  into  elevated  tanks  to 
supply  water  under  pressure  where  it  is  needed  and  for 
fire  protection. 

The  matte  is  tapped  directly  from  the  settlers  into 
lO-ton  pots  which  are  handled  by  an  electric  crane.  The 
first  matte  is  cast  in  molds  on  a  casting  track,  the  sec- 
ond is  delivered  directly  to  the  converters,  of  which 

88 


THOMAS  T.  READ. 

there  are  two,  of  the  cylindrical  or  'trough'  shape. 
These  hold  one  potful  of  matte  and  have  a  hydraulic 
tilting  device  which  is  actuated  by  a  small  Worthington 
pump.  Silicious  ore  is  ground  in  a  pug-mill  with  just 
enough  clay  to  give  it  the  right  consistency,  and  is  then 
used  for  the  converter  lining.  It  is  rammed  into  place 
by  a  1.75  in.  Ingersoll  rock-drill,  which  is  fitted  with 
a  tamping  iron  in  place  of  the  drill  bit.  The  drill  is  sus- 
pended from  a  small  jib-crane,  allowing  ready  adjust- 
ment to  the  work.  The  converter  shells  are  handled  by 
the  electric  crane  and  only  about  ten  minutes  is  re- 
quired to  remove  a  shell  from  its  stall  and  substitute 
another. 

The  slag  is  poured  at  intervals  during  the  blow,  which 
lasts  about  two  hours,  the  progress  of  the  skimming  be- 
ing watched  by  dipping  an  iron  paddle  into  the  issuing 
stream  at  frequent  intervals,  and  noting  when  spots  of 
matte  or  white  metal  appear  on  it.  The  termination  of 
the  blow  is  known  by  the  appearance  and  sound  of  the 
issuing  flame,  as  in  the  bessemerizing  of  steel.  The 
small  amount  of  slag  remaining  on  the  surface  at  this 
stage  is  kept  back  by  throwing  some  of  the  rough  frag- 
ments of  copper  from  the  previous  casting  into  the 
mouth  of  the  converter.  In  this  way  clean  pigs  are  ob- 
tained. Naturally  with  such  a  low-grade  matte  a  great 
deal  of  patching  of  the  lining  is  required,  and  the  lining 
has  to  be  frequently  renewed,  so  that  a  gang  of  men  are 
kept  constantly  busy  preparing  and  applying  converter 
lining.  A  blast  pressure  of  13  lb.,  furnished  by  a  piston 
blower,  is  used  at  the  furnaces. 

The  entire  power  plant  is  of  Allis-Chalmers  design 
and  construction.  Cross-compound  Corliss  engines  at 
145  lb.  steam  pressure  are  used  for  the  blowers.  The 
electric  power  is  furnished  by  a  tandem  compound  Cor- 
liss, which  is  belted  to  a  direct  current,  and  an  alternat- 
ing current  generator,  the  direct  current  being  used  for 
the  tramming  system  and  the  electric  crane,  the  A.-C. 

89 


PYRITE  SMELTING. 

being  used  for  all  other  purposes — as,  for  instance,  the 
driving  of  the  briquetting  machine,  the  furnishing  of 
power  for  the  machine-  and  boiler-shops,  lighting,  etc. 
The  Corliss  engine  has  been  running,  at  120  revolutions 
per  minute,  a  year,  with  only  a  shut-down  of  a  few  min- 
utes each  Sunday.  A  Westinghouse  engine  is  being  in- 
stalled in  order  that  an  accident  to  the  Corliss  may  not 
cause  a  shut-down  of  the  whole  plant.  A  Rand  com- 
pressor supplies  the  air  for  the  tamping  machine  and  for 
pumping  the  artesian  wells. 

The  boiler  plant  consists  of  four  Sterling-  units  deliv- 
ering 1,500  engine  horse-power.  They  are  fitted  with 
Roney  automatic  stokers  and  the  ashes  are  sluiced  away 
along  with  the  slag,  so  that  two  men  are  amply  sufficient 
to  take  care  of  the  plant.  The  Roney  stokers  give  good 
satisfaction,  although  not  an  absolutely  smokeless  com- 
bustion. 

The  briquetting  plant  is  chiefly  interesting  because  of 
the  amount  of  work  it  is  called  upon  to  perform.  Slacked 
lime  is  used  as  the  binding  material  and  a  fair  quality  of 
briquette  is  obtained.  The  method  of  sampling  the 
blister  copper  is  worth  a  passing  note.  The  assay  sam- 
ple is  taken  near  the  middle  of  the  pour.  The  samples 
taken  during  a  day  are  carried  to  the  machine  shop  the 
next  morning  and  cut  completely  in  two  on  a  diagonal 
line  by  a  planer.  From  the  chips  thus  obtained  the  as- 
say sample  is  taken. 

A  little  less  than  200,000  Ib.  of  copper  per  week  is  the 
usual  product  of  the  plant.  It  is  a  great  financial  suc- 
cess, and  thus,  under  the  circumstances,  bears  eloquent 
testimony  to  the  excellence  of  its  design  and  the  effi- 
ciency of  its  management. 

THOMAS  T.  READ. 

Laramie,  Wyo.,  Feb.  16,  1904. 


90 


CONTRIBUTION  BY  HENRY  W.  EDWARDS. 

The  Editor: 

Sir — In  the  current  number  of  the  Journal1  I  see  that 
Mr.  A.  McCharles,  of  Sudbury,  refers  in  a  rather  com- 
plimentary manner  to  the  work  done  some  12  or  more 
years  ago  at  the  smelter  belonging  to  Messrs.  H.  H. 
Vivian  &  Company,  at  the  Murray  mine.  He  is  quite 
right  in  his  main  facts;  and  as  this  plant  was  rather  a 
pioneer  in  a  small  way,  it  may  be  of  interest  to  give  a 
few  particulars  concerning  it. 

To  the  best  of  my  knowledge  and  belief  it  was  the 
first  plant  to  tap  matte  direct  from  the  blast  furnace  to 
the  converter,  and  it  was  there  that  the  first  trough- 
shaped  converter  was  used  in  North  America.  Prof. 
Douglas  in  a  pamphlet  entitled  'Bessemerizing  Copper 
Mattes'  is  good  enough  to  give  the  undersigned  the 
credit  of  being  the  first  to  operate  this  style  of  con- 
verter. 

The  smelter  originally  consisted  of  two  old-style 
round  Piltz  furnaces,  60  in.  diam.,  three  converters,  a 
small  vertical  engine  driving  a  Schicle  fan,  and  a  simple 
horizontal  blowing  engine.  The  idea  of  the  fan  was  to 
produce  a  large  volume  of  blast  with  a  view  to  enrich- 
ing the  matte  by  oxidation  of  a  part  of  the  sulphide  of 
iron  in  the  ore.  However,  one  of  the  Piltz  furnaces  was 
soon  replaced  by  an  oval  furnace  designed  by  the  writer 
with  a  single  eye  to  low  first  cost.  If  I  remember  cor- 
rectly, it  cost  about  $2,000  erected.  Its  greatest  length 
was  about  90  in.,  its  width  33  in.,  with  a  3-in.  water 
space  and  vertical  sides.  It  was  blown  by  a  Baker 
blower,  No.  6,  I  think,  and  its  capacity  was  about  600 
to  800  tons  per  week  of  roast-heap  stuff.  The  matte 

*The  Engineering  and  Mining  Journal,  Feb.  11,  1904,  p.  232. 

91 


PYRITE    SMELTING. 

was  tapped  direct  into  small  trough-shaped  converters, 
each  mounted  upon  a  traveling  blowing  stand;  after 
receiving  its  charge  the  converter  was  moved  along  the 
track  (by  means  of  hand-cranks  operating  gear-and- 
pinion  on  the  driving  wheels)  to  the  blowing-hood.  The 
usual  charge  of  matte  was  about  a  ton  or  a  ton  and  a 
quarter  for  a  converter  with  a  fresh  lining ;  with  an  old 
lining  they  would  take  three  tons  and  over.  Blowing 
was  continued  until  practically  all  the  iron  was  oxidized, 
the  product  being  a  copper-nickel  matte  containing  very 
small  amounts  of  iron  sulphide.  The  converter  slags 
usually  assayed  2  per  cent  nickel,  and  over,  and  were 
returned  to  the  blast  furnace. 

The  plant  was  simple  in  the  extreme;  it  cost  about 
$25,000  or  $30,000;  its  capacity  being  about  600  to  800 
tons  of  burnt  ore  per  week,  in  addition  to  taking  care 
of  all  the  converter  slags.  It  cost  to  operate  about  $2,- 
ooo  per  week,  including  roast-heaps.  About  half,  or 
rather  more,  of  this  was  for  fuel.  The  cost  per  ton  of 
ore  for  the  whole  series  of  operations,  burning,  smelt- 
ing and  converting,  was  about  $3  on  an  average,  in- 
cluding all  the  ordinary  repairs  and  renewals. 

The  ore  was  very  low  grade,  running  about  1.5  per 
cent  nickel  and  about  0.75  per  cent  copper,  so  that  I 
had  to  be  very  careful  not  to  let  the  slag  assays  run  too 
high.  I  am  glad  to  hear  from  Mr.  McCharles  that  they 
have  not  yet  been  beaten  in  the  district. 

At  the  time  this  plant  was  running  the  price  of  nickel 
was  about  half  the  nominal  quotation  of  to-day;  this, 
coupled  with  the  cost  of  mining,  the  small  scale  of  op- 
erations and  the  disadvantage  of  an  administration  4,000 
miles  away,  all  combined  to  make  the  venture  rather 
discouraging ;  and  after  some  four  years  of  existence  it 
was  finally  given  up.  If  current  prices  of  nickel  could 
be  guaranteed  it  would  pay  to  reopen  the  property,  as 
there  is  still  in  the  mine  plenty  of  ore  of  the  grade  then 

92 


HENRY  W.  EDWARDS. 

worked.  Very  little  work  was  ever  done  underground 
below  50  ft.  and  none  at  all  below  100  ft.  During  the 
year  1892  I  tried  there  several  experimental  runs  with 
crude  ore,  the  more  modern  'pyritic'  smelting,  in  fact ; 
but  the  results  were  not  at  all  satisfactory,  chiefly  ow- 
ing to  the  failure  to  get  a  matte  of  suitable  grade  for 
the  converters. 

The  ores  of  the  Sudbury  district  in  general,  and  of 
the  Murray  mine  in  particular,  consist  mainly  of  mas- 
sive pyrrhotite  with  a  gangue  of  gabbro  or  diabase.  Both 
these  rocks  are  comparatively  fusible.  As  a  consequence 
smelting  took  place  so  rapidly  that  there  was  little  op- 
portunity for  oxidation  beyond  that  necessary  to  gen- 
erate the  heat  of  fusion.  The  use  of  silicious  material 
as  a  retarder  was  not  attempted. 

In  this  instance  hot  blast  would  have  been  a  detri- 
ment rather  than  an  advantage. 

A  little  coke  was  used  along  with  the  cold  blast.  The 
fuel  was  not  added  regularly  but  in  occasional  doses 
preceding  and  following  a  slag  charge,  in  order  to  re- 
vive the  furnace  when  the  pyrite  action  seemed  to  wane. 
The  concentration  was  only  about  two  or  two  and  a  half 
into  one,  and  no  attempt  was  made  at  re-concentration 
in  the  blast  furnace  before  blowing  in  the  converters. 

Another  question  also  presented  itself:  sulphur  not 
being  a  reducer  for  nickel  oxide,  would  not  nickel  enter 
the  slag  if  oxidation  were  pushed  too  far?  As  the  main 
object  of  the  operation  was  the  recovery  of  the  nickel 
I  was  a  little  timid  in  running  too  close  to  the  limit. 
There  is  no  reaction  between  nickel  sulphide  and  nickel 
oxide  analogous  to  that  between  copper  sulphide  and 
copper  oxide.  There  seems,  however,  to  be  a  partial 
action  between  copper  sulphide  and  nickel  oxide  which 
demands  closer  investigation. 

HENRY  W.  EDWARDS. 
Grand  Junction,  Colo.,  Feb.  17,  1904. 

93 


CONTRIBUTION  BY  CHARLES  H.  FULTON. 

The  Editor : 

Sir — I  take  pleasure  in  replying  to  the  ten  questions 
submitted  in  regard  to  pyrite  smelting.  I  have  read 
with  much  interest  the  replies  given  to  these  questions 
by  the  metallurgists  taking  part  in  this  discussion,  not- 
ing how  their  experience  compares  with  that  gained  by 
me  at  the  smelting  plant  at  Rapid  City,  South  Dakota. 

1.  What  types  of  ores  are  suited  to  the  process? 

Ores  containing  sufficient  sulphides  of  iron,  either 
pyrite,  pyrrhotite,  etc.,  or  copper  sulphides  are  suitable ; 
also,  probably,  arsenical  pyrite.  The  question  is,  how- 
ever, a  wide  one,  for  ores  partially  oxidized  and  contain- 
ing but  little  sulphur  can  be  handled  without  difficulty. 
A  rather  exceptional  case  is  presented  by  the  practice 
at  Rapid  City  and  Deadwood,  where  the  dry  silicious 
ore  of  the  Black  Hills  is  smelted  with  barren  pyrite, 
limestone  and  a  little  copper  ore.  It  might  be  said  that 
any  ore  mixture  containing  sufficient  sulphur  to  form 
matte  with  iron  and  copper,  and  with  sufficient  silica 
to  form  a  rather  high  silicious  slag,  is  suitable.  But  lit- 
tle or  no  lead  and  but  little  zinc  should  be  present.  Any 
lead  present  would  be  lost,  aside  from  causing  heavy 
silver  losses. 

2.  Is  hot  blast  advisable  ? 

Regarding  the  saving  of  fuel  by  the  employment  of 
hot  blast  I  cannot  speak  from  experience.  At  Rapid 
City,  what  might  be  called  a  warm  blast  is  used,  the 
blast  being  heated  in  a  U-pipe  stove  placed  in  the  dust- 
chamber  directly  below  the  downtakes.  The  tempera- 
ture of  the  blast  is  usually  about  130°  F.,  not  enough  to 
materially  affect  the  fuel  consumption.  Hot  blast,  how- 
ever, possesses  one  notable  advantage,  increasing  the 

94 


CHARLES  H.  FULTON. 

oxidizing  effect  of  the  furnace,  permitting  a  greater  de- 
sulphurization  and  hence  a  higher  concentration.  This 
may  become  a  vital  point  in  the  smelting  of  low-grade 
ores. 

3.  To  what  extent  can  fuel  be  eliminated! 

I  have  no  experience  on  this  point.  In  the  Black  Hills 
the  production  of  highly  silicious  slags,  with  the  feed- 
ing of  just  enough  pyrite  to  furnish  iron  for  the  slag 
and  matte,  and  sulphur  for  the  matte,  calls  for  consid- 
erable fuel.  Also,  the  grade  of  coke  used,  for  the  most 
part  Wyoming  coke  containing  30  per  cent  ash,  aside 
from  being  but  loosely  coherent,  precludes  much  experi- 
mentation on  this  point.  The  amount  of  fuel  consumed 
amounts  to  about  12  to  14  per  cent  of  good  eastern 
coke. 

4.  What  amount  of  copper  is  needed  for  the  collection  of 
the  precious  metals  ? 

That  depends  upon  what  amount  of  slag  loss  the  plant 
can  stand.  It  is  evident  that  when  only  the  silicious  ore 
going  into  the  furnace  is  productive,  and  the  limestone 
and  pyrite  being  added  are  barren,  the  slag  loss  per  ton 
must  be  very  low.  At  Rapid  City  it  was  endeavored  for 
some  time  to  smelt  without  copper  ore,  with  the  result 
that  the  slags  would  invariably  run  from  $1.50  to  $2.50 
in  gold  and  0.5  oz.  silver.  The  addition  of  copper  ore 
immediately  remedied  this.  Copper  ores  are  procured 
from  Montana,  and  are  added  in  just  sufficient  quantity 
to  give  the  desired  result.  The  minimum  amount  of 
copper  added  is  I  Ib.  for  every  one  ounce  of  gold  pres- 
ent in  the  charge,  and  more  if  available. 

The  first  matte  made  usually  contains  from  10  to  14 
per  cent  copper,  4  to  5  oz.  gold,  and  6  to  8  oz.  silver. 
This  is  re-smelted  twice,  until  the  shipping  matte 
reaches  a  value  of  20  to  22  per  cent  copper,  17  oz.  gold 
and  22  oz.  silver.  The  re-smelting  of  the  matte  also  fur- 
nishes somewhat  more  copper  for  some  of  the  charges. 

95 


PYRITE    SMELTING. 

The  loss  of  silver  becomes  very  noticeable  when  the 
copper  contents  of  the  matte  drop  below  8  to  10  per 
cent.  In  my  opinion  few  plants  can  smelt  without  any 
copper  ore. 

5.  What  percentage  of  lime  is  necessary  to  a  clean  slag"? 
Lime  is  necessary  for  a  mechanically  clean  slag1,  that 

is,  a  slag  free  from  entangled  matte.  Lime  reduces  the 
specific  gravity  of  the  slag,  letting  the  matte,  low  in  spe- 
cific gravity,  settle  out  completely.  The  amount  of  lime 
in  the  slag  depends  upon  local  conditions.  At  Rapid 
City  the  slag  made  has  the  following  composition :  CaO, 
28  per  cent;  FeO,  18  per  cent;  A12O3,  4  to  5  per  cent; 
SiO2,  49  to  50  per  cent.  Some  of  the  lime  could  be  re- 
placed with  profit  by  magnesia  up  to  8  or  10  per  cent. 
Lime  slags  of  the  composition  quoted  flow  very  freely 
and  smoothly  from  the  furnace,  and  allow  a  perfect  sep- 
aration of  the  matte.  High  silicious  slags  of  this  type, 
when  produced  with  copper  in  the  furnace,  are  very 
clean.  They  usually  carry  20  to  3OC.  in  gold  and  0.2  oz. 
silver. 

6.  What  percentage  of  sine  in  the  charge  can  be  treated 
profitably  ? 

I  have  no  experience  with  zinc  in  pyrite  smelting. 

7.  What  is  the  degree  of  desulphurization  attainable"? 
At  Rapid  City  the  desulphurization  is  between  75  and 

80  per  cent  of  the  total  sulphur  in  the  charge.  I  believe 
a  greater  degree  of  desulphurization  could  be  obtained 
if  necessary.  The  furnaces  used  contract  but  little  at 
the  tuyeres  and  have  a  strongly  oxidizing  action.  The 
matte-fall,  with  this  desulphurization,  amounts  to  be- 
tween 4  and  5  per  cent  of  the  total  charge.  This  is  found 
amply  sufficient  for  the  collection  of  the  values,  giving 
a  clean  slag. 

8.  What  are  the  possibilities  as  to  capacity  of  furnace  ? 
This  is  less  than  with  furnaces  running  on  partially 

96 


CHARLES  H.  FULTON. 

roasted  ores.  A  38  by  144-in.  furnace  will  take  about 
150  tons  of  burden  per  24  hours,  with  a  considerable 
amount  of  fine  present.  With  good  lump  ore  and  good 
coke,  a  furnace  of  the  above  size  should  take  200  tons. 

9.  What  are  the  limitations  of  the  process  ? 

Pyrite  smelting  is  limited  to  the  ores  discussed  un- 
der the  first  question. 

10.  What  is  the  relative  economy  as  compared  to  rival 
processes ? 

That  depends  much  on  local  conditions.  At  present 
the  pyrite  smelting  plants  of  the  Black  Hills  could  not 
profitably  handle  silicious  ore  of  less  than  $15  per  ton, 
bearing  in  mind  that  this  is  the  only  productive  mate- 
rial going  into  the  furnace.  In  other  districts,  where 
conditions  are  more  favorable  as  regards  fuel  and  ore 
supply,  pyrite  smelting  would  seem  to  be  a  serious  rival 
of  other  smelting  processes,  of  water  concentration, 
and,  indeed,  of  chlorination  and  cyanidation,  for  even 
comparatively  low-grade  ores,  on  account  of  the  high 
saving  made. 

CHARLES  H.  FULTON. 
Rapid  City,  S.  D.,  Feb.  8,  1904. 


97 


CONTRIBUTION  BY  P.  WISEMAN. 

The  Editor: 

Sir — In  your  issue  of  February  4th  you  have  an  edi- 
torial entitled  Tyrite  Smelting1/  and  Mr.  Godshall  pre- 
sents an  interesting  contribution  upon  the  same  sub- 
ject.1 You  make  the  suggestion  that  this  term  be  used 
when  referring  to  the  "oxidizing  smelting  of  pyrite  ores 
in  a  shaft  furnace."  Such  designation  would  probably 
be  more  satisfactory  than  'raw  sulphide'  smelting1,  but 
in  reviewing  the  reasons  given  it  seems  to  me  that  even 
'pyrite'  smelting  does  not  fittingly  describe  the  opera- 
tion. In  the  minds  of  those  interested  in  the  smelting  of 
copper  sulphide  ores  there  are  indelibly  associated  with 
the  word  'bessemer'  the  oxidation  of  sulphur  and  iron, 
and  the  utilization  of  the  heat  thus  g-enerated.  As  this 
is  the  chemistry  of  the  process  which  has  been  vari- 
ously referred  to  as  'pyritic/  'sulphide/  'raw  sulphide/ 
'matte'  and  'pyrite'  smelting,  it  would  seem  more  ap- 
propriate to  speak  of  it  as  'bessemer'  smelting1,  and  I 
would  therefore  suggest  the  use  of  that  term. 

This  designation  describes  the  process  and  at  the 
same  time  implies  the  character  of  the  material  treated, 
and  likewise  the  product  of  that  treatment,  at  least 
when  converting  is  the  last  stage  of  the  process.  The 
term  would  seem  to  be  both  comprehensive  and  distinc- 
tive. It  is  broad  enough  to  cover  every  type  of  ore 
from  which  enough  heat  can  be  generated  by  the  oxida- 
tion of  its  sulphur  (and  iron)  contents  to  do  away  en- 
tirely, or  as  far  as  possible,  with  the  use  of  carbon- 
aceous fuel  in  shaft-furnace  smelting.  If  further  ex- 
planation is  desired  one  can  speak  of  bessemer  smelt- 
ing of  pyrite,  pyrrhotite,  chalcopyrite,  etc.  Confusion 

iThe  Engineering  and  Mining  Journal,  Feb.  4. 1904,  pp.  188  and  192. 

9£ 


P.  WISEMAN. 

can  scarcely  arise  on  account  of  the  bessemerizing  of 
matte,  as  this  operation  is  almost  universally  spoken  of 
as  'converting/  and  as  for  the  product,  it  is  certainly 
none  the  less  bessemer  copper  because  the  same  reac- 
tion has  been  employed  in  each  operation  throughout 
the  process. 

The  use  of  this  term  would  not  necessarily  imply 
that  carbonaceous  fuel  was  entirely  eliminated,  but  that 
as  full  use  as  possible  was  made  of  the  heat  caused  by 
the  oxidation  of  the  sulphur  (and  iron)  contents  of  the 
charge.  Bessemer  smelting  would  have  reference  to  an 
oxidizing  reaction  only.  Mr.  Godshall  calls  attention  to 
the  fact  that  the  term  'raw  sulphide'  smelting  is  par- 
ticularly inappropriate  in  cases  where  the  sulphur  con- 
tent is  so  low  that  it  becomes  necessary  to  maintain 
a  reducing  atmosphere  in  order  to  obtain  a  matte  prod- 
uct. In  such  instances  the  term  'bessemer'  smelting 
would  not  be  proper,  and  the  operation  would  probably 
continue  to  be  spoken  of  as  simply  'matte  smelting/  If 
it  were  desired  to  make  a  further  distinction  between 
the  processes  of  matte  smelting,  the  expression  'bes- 
semer matte'  smelting  would  answer  for  the  oxidizing 
method. 

Bessemer  smelting  may,  therefore,  be  defined  as  fol- 
lows :  Bessemer  smelting  is  the  smelting  of  heavy  raw 
sulphide  ores  in  a  blast  furnace,  by  means  of  an  oxid- 
izing atmosphere,  and  the  utilization  of  the  heat  gener- 
ated by  the  oxidation  of  the  sulphur  and  iron  contents 
of  the  charge  to  reduce  to  a  minimum,  or  entirely  do 
away  with,  the  use  of  carbonaceous  fuel. 

With  regard  to  the  use  of  hot  blast,  its  apparent 
advantages  at  the  plants  where  it  has  been  put  in  use  do 
not  seem  to  have  received  from  those  interested  in 
smelting  the  careful  consideration  they  would  seem  to 
deserve.  That,  under  the  conditions  prevailing  at  some 
of  the  plants,  the  use  of  hot  blast  has  been  a  commercial 
success  will  probably  not  be  questioned.  It  is  not  just 

99 


PYRITE  SMELTING. 

* .  '       . 

to  condemn  hot  blast  unless' a  test  of  both  hot  and  cold 

blast  has  been  made  upon  the  same  ore,  and  under  con- 
ditions fair  to  both,  and 'the  hot  blast  has  failed  to  Rive 
the  desired  or  expected  results.  That  upon  another 
ore,  and  possibly  under  the  most  favorable  conditions, 
one  has  been  able  to  smelt  with  as  little  coke  and  with 
as  large  a  capacity  per  square  foot  of  hearth  area  as 
some  one  else  using  hot  blast  is  simply  negative  evi- 
dence. Possibly  the  use  of  hot  blast  might  have  given 
even  more  favorable  results.  It  is  unusual  for  a  pro- 
cess to  give  equally  satisfactory  results  upon  all  ores; 
the  process  must  be  adapted  to  the  ore  and  the  working 
conditions.  It  seems  reasonable  to  suppose  that  with 
fuel  considerably  cheaper  than  coke  it  would  be  less  ex- 
pensive to  heat  the  blast  outside,  instead  of  inside,  the 
furnace,  and  that  with  the  probable  reduction  in  the 
quantity  of  coke  used,  the  ore  capacity  of  the  furnace 
would  be  increased.  However,  in  heating  outside  the 
furnace  the  problem  is  to  avoid  excessive  losses  from 
radiation  and  otherwise,  but  when  attention  is  given  to 
this  matter  it  probably  will  be  satisfactorily  solved.  I 
have  seen  no  data  as  to  the  test  of  hot  blast  at  Butte, 
but  I  have  the  impression  it  was  found  unsatisfactory 
because  the  saving  of  coke  effected  was  offset,  or  more 
than  offset,  by  the  expense  of  heating  the  blast  out- 
side the  furnace.  At  the  time  the  test  was  conducted 
were  efficient  steps  taken  to  prevent  excessive  losses  by 
radiation  in  the  hot-blast  stove?  At  all  smelting  plants 
there  is  a  great  amount  of  heat  going  to  waste,  and  it 
would  seem  that  every  smelter  superintendent  should 
make  an  effort  to  use  this  waste  heat  in  the  heating  of 
the  blast,  or  for  some  other  purpose.  If  the  installation 
of  boilers  in  connection  with  reverberatory  furnaces,  at 
Anaconda,  proves  satisfactory,  it  is  a  distinct  advance. 
While  the  utilization  of  escaping  furnace  gases  might 
not  heat  the  blast  to  as  high  a  temperature  as  might  be 
desired,  it  is  probable  the  gain  would  be  sufficient  to 

100 


P.  WISEMAN. 

more  than  pay  interest  upon  any  expenditure  for  appa- 
ratus installed.    .  n(J 

I    understand    that    Mr.    J.    Parke    Channjng    has 
been  experimenting  at  Ducktown,  with  the  object  of 
doing  away  entirely,  or  nearly  so,  with  the  use  of  car- 
bonaceous fuel,  and  that  he  has  met  with  very  consider- 
able success.     His  experiments  may  have  included  the  ^ 
use  of  hot  blast.     Perhaps   Mr.   Channing  will  favor 
your  readers  with  his  results?    They  would  certainly  be .. 
of  very  great  interest  in  the  consideration  of  this  sub- 
ject. 

I  have  been  informed  of  one  plant  where  the  use  of 
hot  blast  has  reduced  the  coke  consumption,  about  25 
per  cent.  A  part  of  the  charge  consisted  of  roasted 
ore,  and  when  raw  ore  is  substituted  for  this  it  is.  ex- 
pected the  coke  consumption  will :  :be  stilj  further  re- 
duced. I  hope  to  be  able  soon  to  give  detailed  informa- 
tion as  to  the  results  at  this  plant.  ..  .,  .  , 

In  the  latter  part  of  his  article  Mr.  Godshall  goes  into, 
the  relative  economy  of  the  different  methods  of  treat- 
ing ores,  and  mentions  that  Messrs.  Carpenter  and 
Lang-  both  advocate  the  direct  smelting,  without  con- 
centration, of  the  Butte  ores.  When  one  hears  of  the; 
very  low  smelting  costs  which  are  said  to  prevail  at 
some  of  the  Montana  plants  the  question  very  naturally 
arises  whether  or  not  the  present  methods  could  be  ad- 
vantageously changed.  The  costs  of  smelting  in  re- 
cent years  have  certainly  been  very. materially :redufeld. 
Years  ago  the  costs  of,  and  the  losses  in,  concentration 
were  considerable,  and  if  the  costs  and  losses  of  those 
days  are  being  figured  against  the  low  smelting  costs 
of  to-day,  the  advantage,  assuming  a  favorable  smelting 
mixture,  would  possibly  be  with  straight  smelting.  But 
it  is  possible,  and  probable,  that  the  costs  and  losses  in 
concentrating  have  likewise  been  very  much  decreased, 
thus  lessening  any  advantage  straight  smelting  might 
seem  to  have.  Furthermore,  the  concentrating  ores 


PYRITE    SMELTING. 

contain  such  a  percentage  of  silica  that  a  large  tonnage 
of  expensive  flux  would  be  required,  and  the  amount 
of  first-class  ore  going  into  the  charge  would  not 
greatly  alter  the  composition  percentages.  It  therefore 
seems  unlikely  that  straight  smelting  would  prove  to  be 
any  economy  over  the  method  in  vogue.  It  has  oc- 
curred to  me,  however,  that  possibly  a  larger  tonnage 
of  the  low-grade  ores  is  being  concentrated  than  is  ab- 
solutely necessary  for  a  desirable  smelting  charge,  but 
only  those  who  have  all  the  facts  which  would  have  to 
be  taken  into  consideration  can  determine  this. 

Mr.  Godshall  suggests  that  instead  of  attempting 
straight  smelting,  "it  would  be  better  to  first  demon- 
strate the  advantage,  if  there  be  any,  of  smelting  the 
present  Butte  charge  raw  or  without  any  previous  roast- 
ing." I  do  not  recall  that  roasted  concentrates  go  to 
the  blast  furnace.  The  expense  of  briquetting  the  fine 
concentrates  satisfactorily  is  so  great  that  they  are  pref- 
erably roasted  and  treated  in  the  reverberator^  fur- 
naces with  comparatively  slight  losses  in  flue-dust.  I 
think  in  the  present  practice  the  blast-furnace  charge  is 
'raw/  and  probably  the  only  changes  which  can  be 
looked  forward  to  will  be  the  utilization  of  the  heat 
value  of  the  sulphur  in  this  charge,  if  the  sulphur  con- 
tents will  permit,  and  the  use  of  a  heated  blast. 

P.  WISEMAN. 
Los  Angeles,  Cal.,  Feb.  12,  1904. 


102 


CONTRIBUTION  BY  W.  H.  NUTTING. 

The  Editor: 

Sir — The  term  'raw'  smelting  certainly  defines  itself 
and  covers  a  great  variety  of  ores,  while  'pyrite'  smelt- 
ing has  some  distinctive  features,  and  is  more  restricted 
in  its  application,  so  that  the  latter  term  can  hardly  be 
avoided. 

When  the  ore  treated  has  sufficient  iron  sulphide  to 
become  a  decided  factor  in  replacing  carbonaceous  fuel 
by  the  rapid  oxidation  of  these  elements  in  the  blast  fur- 
nace, thereby  generating  enough  heat  to  do  away  with 
all,  or  a  large  part,  of  the  carbonaceous  fuel  which  would 
be  necessary  in  the  absence  of  these  elements  in  excess 
of  the  amount  required  for  the  composition  of  matte 
showing  the  required  concentration,  pyrite  smelting — 
as,  possibly,  the  most  distinct  process — merges  into 
smelting  for  matte  without  any  great  excess  of  sulphur 
and  iron  to  be  used  as  fuel,  and  thence  into  copper 
smelting,  with  so  little  sulphur  present  that  it  does  not 
need  to  be  considered  as  a  factor  in  the  running  of  the 
furnace  or  the  composition  of  the  product.  I  believe 
that  the  questions  under  consideration  apply  more 
nearly  to  pyrite  smelting. 

I.  What  types  of  ores  are  suited  to  the  process! 

Iron  sulphide  ores — the  purer  the  better — combined 
with  silicious  ores;  and  if  both  are  free  from  fine  the 
conditions  are  ideal,  especially  if  the  charge  is  free  from 
zinc  sulphide.  Under  these  conditions  most  of  the 
claims  made  by  the  most  enthusiastic  advocates  of 
pyrite  smelting  could  be  verified,  but,  unfortunately,  all 
these  favorable  conditions  seldom  exist  in  any  one 
locality,  and  the  question  arises:  What  percentage  of 
fine  and  zinc  sulphide  makes  the  ore  unsuitable? 

103 


PYRITE  SMELTING. 

Or,  in  other  words :  At  what  point  would  some  other 
method,  or  combination  of  methods,  be  competitive?  I 
think  that  each  separate  smelting  proposition  has  to  be 
figured  out  from  existing  local  conditions,  such  as  the 
physical  character  of  the  ore,  the  cost  of  coke  and 
fluxes,  etc.  Ores  containing  lead  are  not  suitable  for 
various  commercial  reasons,  though  this  element  does 
not  interfere  with  the  process  in  other  respects. 

2.  Is  hot  blast  advisable? 

Every  metallurgist  should  be  guided  by  local  con- 
ditions as  to  the  advantage  to  him  of  a  heated  blast 
from  a  commercial  standpoint.  Metallurgically  I  be- 
lieve it  is  always  an  advantage ;  but  the  question  of  get- 
ting a  heated  blast  at  a  cost  showing  any  additional 
profit  over  the  use  of  the  necessary  amount  of  coke,  at 
Utah  and  Colorado  prices,  has  never  been  satisfactorily 
demonstrated  to  me,  either  by  my  own  experience  or 
that  of  others.  The  conditions  affecting  the  compara- 
tfve  cost  are  the  amount  of  fine  and  zinc  sulphide  in  the 
charge,  together  with  the  price  of  coke. 

~  3.  To  what  extent  can  fuel  be  eliminated"? 

With  a  coarse  charge,  together  with  other  true  pyritic 
qualifications  as  to  sulphur  and  iron,  coke  can  be  elimi- 
nated in  proportion  to  the  absence  of  fine  and  zinc  sul- 
phide, down  to  the  intermittent  use  of  two  or  three  per 
cent. 

4.  What  amount  of  copper  is  needed  for  the  collection  of 
the  precious  metals  ? 

In  the  absence  of  zinc  sulphide  a  fairly  satisfactory  re- 
covery of  the  precious  metals  can  be  made  in  an  iron 
matte  withput  copper,  but  the  beneficial  effect  of  even 
0.5  per  cent  copper  in  the  charge  will  be  recognized ;  and 
if  the  charge  contains  a  considerable  amount  of  zinc  sul- 
phide, 1.5  to  2  per  cent  copper  becomes  necessary  for  a 
good  separation,1  as  a  reasonable  difference  in  the  spe- 

104 


W.  H.  NUTTING. 

cific  gravity  between  the  matte  and  slag  must  be  main- 
tained. 


5.  What  percentage  of  lime  is  necessary  to  a  clean 

The  amount  of  lime  necessary  is  governed  by  'the 
amount  of  available  iron  for  the  silica  in  the  charge. 
When  the  iron  is  sufficient  to  satisfy  both  the  matte 
requirements  and  the  silica,  very  little  lime  is  necessary, 
and  may  be  cut  down  to  six  or  eight  per  cent.  In  the 
case  of  insufficient  iron,  lime  can  be  used  as  a  basJe 
with  which  to  combine  the  silica,  to  a  considerable  ex- 
tent. I  find  that  under  my  present  conditions  here  the 
following  composition'  of  slag  works  well  in  every  re- 
spect :  FeO,  28  per  cent  ;  CaO,  18  per  cent  ;  SiO2,  44  per 

cent  ;  Ag,  0.24  oz.  ;  Cu,  0.22  per  cent. 

•  "    "    '  -  * 

6.  What  percentage  of  zinc  in  the  charge  can  be  treated 

profitably  ? 

This  element,  in  the  form  of  sulphide,  is  an  unmiti- 
gated nuisance.  Its  bad  effects  are  numerous,  and  will 
be;  ndted  in  the  tonnage,  recovery  and  product.  Diffi- 
culties start  with  as  little  as  three  per  cent  in  the  charge, 
and  increase  quite  in  proportion  until  12  per  cent  is 
reached,  when  the  bad  effects  become  serious,  scaffold- 
ing the  furnace  shaft  and  forming  accretions  at  the  bot^ 
torn  of  the  furnace,  sump  and  fore-hearth.  The  accu^ 
mulation  on  the  bottom  of  the  furnace  continues,  if  not 
corrected,  until  the  tuyeres  are  slagged,  at  which  point 
the  furnace  is  likely  to  go  out  of  business  for  a  few  days. 
If  taken  in  time,  and  the  zinc  in  the  charge  reduced,  with 
the  addition  of  scrap  iron,  the  furnace  can  generally  be 
nursed  into  good  condition  again.  ,  r 

,  Zinc,  requires  additional  fuel  and  iron,  .  reduces  the 
tonnage  treated,  causes  volatilization  of  silver,  both  in 
the  .furnaces  and  converters  (if  blistered  copper  is  the* 
final  product),  increases  the  specific  gravity  of  the  slag 
'and  decreases  that  of  the  matte,  thereby  making  the" 
separation  less  perfect,  and  reduces  the  value  of  the' 

105 


PYRITE   SMELTING. 

matte,  whether  sold,  re-treated,  or  converted,  and  will 
show  a  very  marked  increase  in  silver  losses  in  the 
slag. 

7.  What  is  the  degree  of  de sulphur ization  attainable? 
Under  conditions  which  warrant  the  choice  of  this 

process,  the  smelting  is  rapid  and  the  elimination  of 
sulphur  is  from  60  to  70  per  cent,  with  a  concentration 
of  6  or  7  into  i.  A  much  higher  degree  of  desulphur- 
ization  could  be  attained,  but  it  would  be  at  the  expense 
of  tonnage,  either  by  slower  driving,  or  by  a  more  sili- 
cious  charge.  In  either  case,  the  tonnage  would  be  less. 

8.  What  are  the  possibilities  as  to  capacity  of  furnace"! 
The  capacity  of  a  furnace  means  the  number  of  tons 

of  ore  put  through  in  24  hours,  and  the  possibilities  in 
this  direction  are  governed: 

First,  by  the  amount  of  fluxes  necessary  to  the  ore 
charge. 

Second,  by  the  percentage  of  fine  in  the  charge. 

Third,  by  the  amount  of  zinc  sulphide  present  in  the 
charge;  assuming  that  other  conditions  are  compara- 
tive. 

I  believe  that  the  limit,  as  regards  hearth  area,  and 
volume  and  pressure  of  blast,  have  been  reached,  and 
that  new  records  will  depend  upon  the  character  of  the 
charge. 

9.  What  are  the  limitations  of  the  'process  ? 
Competitive  processes,  or  combination  of    methods, 

showing  greater  profits,  governed  to  a  great  extent  by 
fine,  zinc  sulphide  and  cost  of  coke. 

10.  What  is  the  relative  economy  as  compared  to  rival 
processes  ? 

Less  expensive  construction  of  plant,  less  handling 
of  material,  less  fuel  required.  Absence  of  roasting, 
either  in  mechanical  roasters,  which  require  crushing 

loe 


W.  H.  NUTTING. 

and  rolling  of  the  ore,  or  heap  roasting,  with  its  attend- 
ant handling  and  loss;  and  fuel  used  in  either  case. 
Large  tonnage  and  rapidity  of  work,  which  means  less 
operating  cost  per  ton  of  ore.  The  resulting  slags  can 
be  very  silicious,  if  necessary  up  to  46  per  cent,  without 
greatly  retarding  the  speed  of  the  furnace,  and  are  com- 
paratively clean.  The  sulphur  excess  in  the  charge  is 
naturally  a  safeguard  in  taking  care  of  the  copper,  pre- 
venting the  formation  of  oxides  which  might  enrich  the 
slag. 

In  conclusion,  I  wish  to  confirm  the  experience  of 
other  operators  in  regard  to  the  delicacy  of  the  process. 
The  care  and  continual  watchfulness  increase  as  the  car- 
bonaceous fuel  is  decreased,  and  any  stop  at  all  affects 
the  furnace  for  hours,  and  long  campaigns  are  the  ex- 
ception. 

W.  H.  NUTTING. 
Bingham  Junction,  Utah,  Feb.  28,  1904. 


107 


RAW  SULPHIDE  SMELTING  AT  DUCKTOWN. 

BY  W.  K.  FREBLAND. 

The  following  facts,  figures,  and  observations  are  in- 
tended to  contribute  something  to  the  practical  side  of 
a  subject  the  literature  of  which  is,  unfortunately,  still 
largely  that  of  theory  and  desultory  experiment. 

The  work  described  here  was  done  at  the  works  of 
the  Ducktown  Sulphur,  Copper  and  'Iron  Company, 
Limited,  at  Isabella,  Tennessee,  under  the  writer's  per- 
sonal supervision.  It  covered  a  period  of  several 
months,  the  first  of  which  was  productive  of  little  else 
than  6  per  cent  matte,  'break-outs,'  and  'chills' — a 
repetition  of  the  writer's  experience  in  earlier  attempts 
here  and  elsewhere.  But  in  the  present  instance,  sup- 
ported and  encouraged  by  a  board  of  progressive  direc- 
tors, and  particularly  by  Mr.  J.  G.  Cordon,  managing 
director,  the  work  was  persisted  in,  and  rewarded  by  the 
measure  of  success  now  recorded;  and  it  may  not  be 
amiss  to  add  here,  that  it  has  been  suspended  only  to 
clean  up  the  stocks  of  roasted  ore  on  hand  before  adopt- 
ing it  permanently.  The  practice  consisted  of  .two 
operations,  carried  out  alternately  in  the  same  furnace : 

1.  The  smelting  of  raw  ore  to  a  low-grade  matte,  in 
the  neighborhood  of  20  per  cent. 

2.  The  re-concentration  of  the  low-grade,  to  a  50  per 
cent  matte. 

Furnace,  etc. — A  Herreshoff  furnace  was  used,  a  gen- 
eral description  of  which  may  be  found  in  Peters'  'Mod- 
ern Copper  Smelting/  It  has  a  total  depth  of  8.5  ft., 
with  a  cross-sectional  area,  at  tuyeres,  of  21.7  sq.  ft. 
The  regular  Herreshoff  forehearth,  proving  trouble- 
some, was  replaced  by  a  water-cooled,  blast-trapping 
spout,  and  an  ordinary  brick-lined  settler  of  5  ft.  by 
4  ft.  by  18  in.  internal  dimensions.  A  No.  6  Conners- 


W.  H.  FREELAND. 

ville  blower,  driven  by  a  direct-connected  engine,  sup- 
plies the  blast. 

Duration  of  Campaigns.— As  each  locality  presents  its 
own  conditions,  it  is  useless  to  recount  the  preliminary 
difficulties.  Suffice  it  to  say,  that  these  were  overcome, 
when  the  lessons  taught  by  repeated  failures  were 
learned  and  understood.  This  stage  reached,  several 
campaigns  of  from  two  to  six  weeks  wereimade  without 
stoppage  of  blast,  their  duration^  being  limited  only  by 
the  necessity  of  shutting  down  to  wash  out  silt  from 
furnace  jacket,  spout,  etc. 

Test  Run. — One  of  these  campaigns  was  a  test  run, 
differing  from  the  others,  however,  only  in  the  care  be- 
stowed upon  weighing  and  sampling. 

Hourly  samples  were  taken  of  each  constituent  of 
furnace  charge,  also  of  slag  and  matte.  These  were 
combined  into  daily  samples,  and  reduced  to  laboratory 
pulps,  which  in  their  turn  were  combined,  in  propor- 
tions corresponding  to  the  daily  tonnages.  The  final 
samples,  thus  representing  reliable  averages  of  the 
entire  run,  were  carefully  analyzed,  in  duplicate,  by  Mr. 
Thorn  Smith,  a  chemist  whose  abilities  are  known  to 
readers  of  The  Engineering  and  Mining  Journal.  The 
same  care  was  observed  in  the  weighing  of  materials, 
including  flue-dust ;  and  allowances  were  made  for  ma- 
terial in  furnace  at  start  and  finish  of  both  operations, 

The  first  operation  occupied  i6£  days,  smelting  in 
that  period  1,120  tons  ore,  89  tons  quartz,  162  tons  slag; 
1,371  tons  total  burden;  with  38  tons  coke,  the  coke 
being  equivalent  to  3.4  per  cent  of  the  ore,  or  2.77  per 
cent  of  total  burden. 

Ore,  etc. — The  Ducktown  ore,  as  is  well  known,  is  a 
pyrrhotite,  carrying  less  than  3  per  cent  copper,  and  no 
precious  values.  Full  analyses  of  the  ore,  fluxes,  and 
coke  used  in  first  operation,  and  products  therefrom, 
are  given  in  Table  A  (page  HI). 

109 


PYRITE    SMELTING. 


Matte. — The  matte  produced  is  represented  by  396 
hourly  samples.  Ignoring  fractions,  or  calling  any- 
thing over  0.5  a  unit,  and  dropping  all  lesser  fractions, 
the  variations  in  assays  are  shown  as  follows : 

6  samples  assayed  11  per  cent.      24  samples  assayed  24  per  cent. 


4 
16 
38 
30 
36 
28 
34 
39 
28 
31 


14 
15 
16 
17 
18 
19 
20 
21 
22 
23 


20 
20 
9 
10 
14 
7 
1 
1 


25 
26 
27 
2S 
29 
30 
31 
32 


3%  samples  aver'gd  21.18  % 

The  above  numerical  average  is,  of  course,  only  ap- 
proximate (the  true  average  being  20  per  cent).  Call- 
ing all  values  with  less  than  20  occurrences  accidental, 
the  matte  may  be  said  to  have  ranged  from  16  to  26  per 
cent.  The  lower  assays  are  eliminated,  as  they  practi- 
cally all  occurred  at  blowing  in;  and  the  higher  ones, 
because  steps  were  taken  to  reduce  them  as  quickly  as 
detected. 

From  the  foregoing  tonnages,  the  average  charge  is 
readily  calculated.  Based  on  this  and  the  tabulated 
analyses,  a  synthesis  of  the  charge  and  its  products  is 
constructed,  which,  if  somewhat  empirical,  is  neverthe- 
less interesting  and  useful.  See  Table  B  (page  in). 

Reducing  the  constituents  of  the  938.24  Ib.  of  the  cal- 
culated slag  to  percentage  terms,  it  is  seen  to  compare 
very  closely  with  the  actual  slag  analysis,  viz.: 

Comparison  of  Calculated  and  Actual  Slags— First  Operation. 

By  Calculation.        By  Analysis. 


Lb. 

Cu    3.40 

Pe    358.22 

S    15.94 

SiO2 303.89 

CaO    84.20 

MgO    30.30 

Zn    14.11 

AhOs    11.84 

Mn    8.15 

O    * 108.19 


Totals   .  .  938.24 


0.36 

38.18 

1.70 

32.39 

8.97 

3.23 

1.50 

1.26 

0.87 

11.54 

100. 


0°37 
38.84 
1.74 
3260 
8.24 
3.44 
1.54 
1.50 
0.80 
10.88 

99.95 


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W.  H.  FREELAND. 

Second  Operation.— -The  reconcentration  of  the  20  per 
cent  matte  occupied  a  few  hours  less  than  three  days, 
and  smelted,  in  addition  to  the  matte,  34  tons  of  raw 
ore  and  discarded  samplings  from  laboratory;  this  ore 
being  added  to  charge  to  keep  the  tenor  of  final  matte 
from  rising  too  high  for  comfortable  running. 

Analyses,  etc.,  of  second  operation  are  tabulated  as 
follows.  (For  analyses  and  synthesis  of  charge  in 
second  operation  see  Tables  C  and  D  (page  1 12). 

Comparison   of  Calculated   and  Actual   Slags— Second  Operation. 

By  Calculation.        By  Analysis. 

Lb.  %                   % 

Cu 7.13  0.60            0.60 

Fe    520.96  44.07  43.99 

S    14.15  1.20             1.19 

Si02 401.15  33.93  33.72 

CaO    27.66  2.34             2.03 

Mgo   7.25  0.61             U.57 

Zn    23.56  2.00             2.12 

AhOs    17.30  1.46             216 

Mn    6.48  0.55             0  50 

O    156.54  13.24  12  86 


Totals    1182.18  100.  99.74 

Furnace  Capacity. — Including  both  operations,  the 
furnace's  average  daily  capacity  is  60  tons  raw  ore.  Its 
average  on  roasted  ore  may  be  fairly  quoted  at  115  tons, 
hence  a  loss  of  efficiency  of  nearly  48  per  cent.  But  in 
considering  this  feature,  it  must  be  stated  that  granu- 
lated slag  was  used  throughout  the  test  run,  and  that  a 
daily  average,  equivalent  to  80  tons  raw  ore,  has  been 
repeatedly  attained  when  lump  slag  was  available,  thus 
reducing  the  loss  of  efficiency  to  30  per  cent.  It  is 
hoped  that,  with  time  and  experience,  this  loss  will  be 
still  further  reduced.  It  is  highly  probable  that  hot 
blast  would  increase  the  smelting  capacity,  but  with  a, 
furnace  of  the  Herreshoff  dimensions,  the  additional  tax 
for  fuel,  coal-heavers  and  firemen  was  found  prohibi- 
tive. 

Concentration. — It  will  be  seen  that  concentrations 
effected  were  7.3  into  i  by  first  operation,  and  2.5  into, 
I  by  second,  but  these  by  no  means  represent  the  limits 

113 


PYRITE  SMELTING. 

attainable.  Contrary  to  the  experience  of  many,  the 
reconcentration  of  the  first  matte  presents  no  difficul- 
ties at  Ducktown.  There  is  no  limit,  within  the  range 
of  matte,  to  the  second  operation.  A  6  per  cent  matte 
may  be  brought  up  to  a  50  per  cent  quite  as  successfully 
as  any  higher  grade  initial  matte ;  nor  is  this  statement 
based  upon  odd  or  occasional  samples,  but  upon  more 
than  one  car-load  of  matte  so  made. 

Occasional  samples  of  70  per  cent  matte  have  been 
assayed  from  the  reconcentration  of  a  10  per  cent  initial 
matte,  but  such  conditions,  if  permitted  to  continue, 
would  speedily  result  in  a  'chill/  particularly  with  the 
scanty  flow  of  a  small  furnace. 

The  degree  of  concentration,  whether  in  first  or 
second  operation,  is  in  the  main  proportionate  to  the 
speed  at  which  the  furnace  is  driven,  and  is  controlled 
by  the  proportion  of  quartz  on  charge,  or  manipulation 
of  blast,  or  both.  But  on  these  seemingly  simple 
measures,  hinge  not  only  the  grade  of  the  matte,  but  the 
life  of  the  campaign,  and  probably  the  confidence  of 
owners,  if  disasters  occur  too  often  on  first  attempts. 

Furnace  Conditions. — The  average  volume  and  pres- 
sure of  blast  were  4,500  cu.  ft.  free  air  per  minute,  and 
17  oz.,  respectively.  Some  incrustation  forms  around 
the  furnace  top,  but  not  enough  to  be  troublesome.  At 
the  region  of  the  tuyeres,  however,  a  porous  friable 
accretion  bridges  the  furnace  from  wall  to  wall.  Light 
is  rarely  discernible  on  punching  the  tuyeres.  It  may 
seem  unreasonable,  but  is  nevertheless  true,  that  a  bar 
has  been  driven  through  the  furnace,  entering  a  tuyere 
on  one  side,  and  withdrawn  from  the  opposing  tuyere, 
by  the  naked  hand. 

This  condition,  alarming  as  it  would  seem  in  ordinary 
smelting  practice,  is  believed  by  the  writer  to  be  essen- 
tial to  satisfactory  concentration.  The  condition  en- 
countered in  barring  the  tuyeres  leaving  no  doubt  that, 
for  a  certain  area  surrounding  each  tuyere,  the  furnace 

114 


W.  H.  FREELAND. 

is  bridged  from  wall  to  wall,  the  molten  matte  and  slag 
must  find  its  passage  into  the  crucible  through  channels 
between  tuyeres.  If  visible,  a  horizontal  section  of  fur- 
nace at  tuyere  level  would  probably  present  something 
like  the  appearance  shown  in  the  accompanying  dia- 
gram, Fig.  2. 


PIG.  2.    HORIZONTAL  SECTION  OF  FURNACE. 

While  the  horizontal  section  is  hypothetical,  there  is 
no  doubt  as  to  the  vertical  shape  assumed  by  the  accre- 
tion, which  is  found  to  be  as  shown  in  Fig.  I. 

Granting  the  condition  described,  then  the  effect  is; 
the  column  of  charge  resting  upon  boshes  and  bridge, 
undergoing  a  partial  roasting  in  its  descent,  and  a  rapid, 
fierce  oxidation  as  it  reaches  and  is  held  in  the  con- 
stricted channels.  The  charge  sinks  evenly  and  uni- 
formly, rarely  showing  a  hot  top.  The  slags  run  hot 
and  fluid  ;  in  fact,  the  furnace  gives  less  trouble  through- 
out than  those  alongside  smelting  roasted  ore,  a  fact 
testified  to  by  the  furnace  hands  importuning  the  fore- 
man to  "give  them  a  chance"  on  No.  I. 

Coke. — Calculating  the  percentage  of  coke  on  copper- 
bearing  burden  only,  the  regular  charge  of  1,000  Ib. 

115 


PYRITE    SMELTING. 


ore  carries  30  Ib.  coke.  Often  days  will  pass  without 
a  variation  in  charge  sheet.  Occasionally  from  neces- 
sity, but  more  frequently  from  the  foreman's  timidity, 
the  coke  is  doubled  for  an  hour,  or  perhaps  two,  on  a 
shift.  It  is  due  to  these  causes  that  the  average  coke 

W%L_ 


FIG.  1.    VERTICAL.  SECTION   OF  FURNACE. 

percentage  on  this  test  run  is  raised  from  the  nominal 
3  to  3.4  per  cent  of  the  first  operation. 
'  On  the  second  operation,  the  coke  averaged  8  per 
cent  on  matte,  etc.  Calculating  the  coke  of  both  opera- 
tions back  to  the  original  ore,  the  total  coke  consump- 
tion is  4.4  per  cent  thereof. 

Slag  Losses. — Referring  to  the  tables,  slag  losses  are 
seen  to  be  0.37  per  cent  on  first,  and  0.6  per  cent  on 
second  operation.  Calculating  both  back  to  a  basis  of 

116 


W.  H.  FREELAND. 

the  slag  of  the  first  operation,  the  equivalent  is  0.45  per 
cent,  a  loss  that  should  claim  the  attention  of  all  familiar 
with  the  high  concentration  of  a  low-grade  ore,  par- 
ticularly where  settler  area  is  limited  by  a  small  matte 
flow. 

Flue-Dust. — The  flue-du$t  recovered  from  both  opera- 
tions (and  almost  wholly  from  the  first)  was  equivalent 
to  53  Ib.  per  ton  of  original  ore. 

Economcs. — While  it  is  not  within  the  scope  of  the 
present  article  to  go  into  comparative  costs  and  copper 
recoveries,  it  may  be  added  that,  despite  the  greatly  re- 
duced tonnage  capacity  per  furnace,  the  economical  re- 
sult of  raw  ore  smelting  is  gratifying  beyond  all  antici- 
pation.1 


"i  Reprinted  from  The  Engineering  and  Mining  Journal,  May  2,  1908,  p.  664. 

117 


COPPER  LOSSES  IN  BLAST  FURNACE  SLAGS. 

By  WILLIAM  A.   HBYWOOD. 

With  a  view  to  presenting  in  graphic  form  the  ratio 
of  copper  in  blast  furnace  slags  to  the  copper  contained 
in  the  matte  produced  at  the  same  time,  2,590  assays, 
representing  all  the  work  of  two  furnaces  for  a  period 
of  two  and  one-half  years,  were  plotted  with  the  results 
shown  in  the  accompanying  diagrams.  The  first  inten- 
tion was  to  plot  the  slags  to  show  the  copper  contents 
only,  but  it  soon  became  apparent  that  the  amount  of 
silica  in  the  slag  had  a  great  influence  on  the  copper 
contents,  the  more  basic  iron  slags  carrying  away 
much  more  copper  than  the  more  silicious  slags.  As 


0.65 


0.60 


00.55 

CO 

z 

a  0.50 


o 
o 

£0.45 
ui 

O 

• 

^0.40 


afc 


0.35 


030 


25 


30 


35  40  45  50 

PER  CENT  COPPER  IN  MATTE 


FIG.  1.     SLAG   CURVES   REPRESENTING  2,500   ANALYSES. 
TENNESSEE    COPPER    COMPANY,  JAN.  25,  1904. 

the  ore  smelted  was  heap-roasted  pyrrhotite  containing 
only  from  10  to  20  per  cent  of  silica,  and  the  remain- 


118 


WILLIAM  A.  HEYWOOD. 

ing  silica  had  to  be  added  in  the  form  of  barren  quartz, 
it  was  an  important  question  to  determine  what  quan- 
tity of  silica  was  the  most  economical,  considering  the 
rate  of  smelting  and  the  cost  of  converting  matte  of 
different  grades,  as  well  as  the  copper  losses  in  the  blast 
furnace  slags. 

An  impression  exists  at  many  copper  smelters  that  a 
furnace  producing  a  slag  high  in  iron  runs  much  faster 
than  one  running  on  a  more  silicious  mixture.  Within 
the  limits  of  our  practice  this  has  not  been  confirmed. 
Taking  our  largest  runs  of  over  600  tons  per  furnace- 
day,  as  many  have  occurred  when  the  furnace  was  pro- 
ducing a  slag  with  32  to  34  per  cent  silica  as  when  the 
slags  contained  from  28  to  32  per  cent  silica. 

Each  assay  represents  an  average  of  '12  hours  slag 
from  one  furnace.  The  samples  were  taken  hourly, 
chilled,  and  the  copper  determined  on  a  five  gram 
sample  by  cyanide  after  precipitating  the  copper  with 
aluminum.  Once  a  week  composite  samples  were 
made  up  from  the  daily  samples  from  each  furnace  and 
assayed  by  electrolysis.  Part  of  the  weekly  composite 
samples  were  sent  to  New  York  regularly,  for  check 
assay.  The  electrolytic  determination  is  usually  0.02 
per  cent  higher  in  copper  than  the  cyanide  assay.  The 
insoluble  in  the  slag  was  taken  as  silica,  although  the 
absolute  silica  determined  by  fusion  is  1.5  to  2  per  cent 
lower. 

The  following  is  a  complete  analysis  of  a  month's 
average  slag: 

SiOa 31.04  per  cent. 

FeO    51.40     " 

AhOa   4.84 

CaO    • 6.30 

MgO    1.37 

S    1.36 

Zn    2.01 

Mn    0.51 

Cu    0.45 

In  Fig.  i  the  assays  of  the  different  slags  and  mattes 

119 


PYRITE  SMELTING. 

were  first  plotted  separately  for  the  different  silica 
percentages.  The  curves  were  then  traced  on  one 
sheet. 

In  Fig.  2  these  curves  were  adjusted,  and  the  actual 


0301 


25      30     35      4O     45     5O      55      6( 

PER  CENT  COPPER  IN  MATTE 

FIG.  2.    ;COPPER    LOSS    CURVES    FOR    DIFFERENT    SLAGS. 


6 


Based  on  adjusted  slag  curves  and  assumption  that  total  amount 
of  &lag  increases  in  direct  ratio  to  bilica  added  in  form  of  quartz,  as 
follows: 

30%  9:1  ica  =  10.000  slag.  33%  Silica  =  10,447  slag. 

31%  Silica  =  10.145  slag.  34%  Silica  =  10,606  slag. 

32%  Silica  =  10,290  slag. 

copper  losses  are  shown  by  allowing  for  the  increased 
quantity,  of  slag  made  by  the  additional  quartz  neces- 
sary to  produce  the  more  silicious  slag.1 


iReprinted  from  The  Engineering  and  Mining  Journal,  Mar.  10, 1904,  p.  396. 

120 


CONTRIBUTION  BY  E.  A.  WEINBERG. 

The  Editor : 

Sir — I  venture  to  contribute  a  few  observations  to  the 
discussion  on  this  subject,  which  was  resumed  by  Mr.  .- 
Godshall's  letter  in  your  issue  of  February  4,  and  fol- 
lowed on  February  1 1  by  the  contributions  of  Mr.  Will- 
iam A.  Heywood  and  Mr.  G.  F.  Beardsley,  respectively. 

Concerning    the    designation    'pyritic    smelting/    it 
seems  immaterial  whether  we  continue  using  the  term 
or  not,  but  in  my  opinion  it  would  serve  no  purpose  to 
alter  a  technical  term,  which  as  such  has  found  a  place 
in  •. .many  metallurgical  text-books  and  has  become  es- 
tablished by  common  usage.    Its  definition,  according 
to.  recent,  experiences,  has  been  altered  to  the  extent 
that  in  future  we  shall  not  regrard  the  hot  blast  as  one 
of  the  essential  features  in  the  direct  smelting  of  heavy 
sulphide  ores  for  matte.    Mr.  Godshal^  briefly  defines 
'pyritic'  smelting  as  a  form  of  matte  smelting,,  whereby,; 
the  maximum  amount  of  heat  is  derived  from  the  com- 
bustion of  heavy  raw  sulphide  ores  in  a  blast  furnace, 
in  addition ,  to  the  minimum  amount  of  necessary  heat 
obtained  directly; from  carbonaceous  fuel,  an4  I  believe  i 
this  definition  ;will  be  acceptable  to  most  metallurgists. - 
„; Whether  hot  or  cold  blast  should  be  used  will  p rob- j 
ably,  remain  a  question  to  be  determined  by  the  special  •; 
requirements  pf  any  particular  proposition j  though- J^e-1 
cent  experiences  strongly  point  to  the  fact  r that  an  iin-7 
creased  air  supply  for  the  rapid  oxidation  of  the -sulphur: 
andiron  is  all  that  is  required  to  bring  about  the  de- 
sired conditions. 

.With  lower  blast-pressures  and  lower  charges  it  may- 
be possible  that  the  hot-air  blast  has  an  initiative  action, 

121 


PYRITE    SMELTING. 

on  the  combustion  of  the  sulphides,  but,  after  all,  it  is 
not  the  temperature  of  the  air,  but  its  volume,  which  is 
responsible  for  the  reaction  in  pyritic  smelting,  and  for 
the  remarkable  increase  in  the  tonnage  treated.  Any 
metallurgist,  who  has  had  practical  experience  with 
matte  smelting  in  blast  furnaces,  will  be  able  to  recall 
many  instances  when  his  furnaces  would  'drive'  to  such 
an  extent  that  often  the  pots  available  were  insufficient 
to  cope  with  the  slag  flow,  and  the  air-supply  to  the  fur- 
naces had  to  be  reduced  in  consequence.  With  larger 
furnaces,  better  blowers,  and  a  better  equipment  for  the 
handling  of  large  quantities  of  material,  our  aim  to-day 
is  to  obtain  just  those  conditions  which,  not  many  years 
ago,  were  accidentally  produced,  and  almost  considered 
objectionable. 

When  we  compare  the  results  of  the  experimental 
furnace  run  No.  5  with  those  obtained  in  the  run  No.  4, 
Mr.  Heywood's  figures  are  remarkable  for  the  enor- 
mous increase  in  the  tonnage  treated.  A  few  explana- 
tory remarks  from  him  regarding  the  duration  of  these 
experimental  runs  would  no  doubt  be  welcome. 

I  hope  also  that  Mr.  Beardsley,  as  late  metallurgist 
at  Mt.  Lyell,  will  favor  us  with  a  more  conclusive  state- 
ment regarding  the  work  done  at  Mt.  Lyell  with  hot  and 
cold  blast  respectively.  He  already  informs  us  that  the 
recent  practice  at  Mt.  Lyell  has  been  to  discontinue  the 
hot  blast,  from  which  it  would  appear  that  the  manage- 
ment found  it  profitable  to  do  so.  But  even  if  the  blast 
could  be  heated  by  waste-gases,  as  suggested  by  Mr. 
Beardsley,  and  all  other  conditions  remained  the  same, 
it  would  be  of  great  interest  to  know  his  experience  with 
regard  to  the  practical  gain  of  using  heated  air  under 
these  circumstances. 

Mr.  Godshall  quotes  Mr.  J.  W.  Nesmith's  compara- 
tive statement  giving  the  results  of  a  test  run  at  Silver- 
ton,  Colorado.  The  figures  are  not  conclusive,  in  so  far 
as  no  attempt  was  made  to  ascertain  whether  an  in- 

122 


E.  A.  W BIN BERG. 

creased  air-supply  alone  would  have  brought  about  an 
increase  in  the  furnace  capacity. 

Owing  to  a  long  absence  from  the  United  States,  I 
am  not  competent  to  discuss  the  question  concerning 
the  inducements  which  central  localities  like  Denver, 
Pueblo  and  Salt  Lake  may  offer  to  a  matte  smelting  es- 
tablishment to  compete  with  lead  smelters  in  the  market 
for  dry  ores.  The  question,  in  my  opinion,  is  certainly 
not  to  be  settled  by  the  mere  cost  of  smelting  per  ton 
of  ore,  as  in  addition,  cost  of  refining  and  realization 
charges  would  have  to  be  taken  into  consideration. 

E.  A.  WEINBERG. 
London,  March  2,  1904. 


CONTRIBUTION  BY  WALTER  E.  KOCH. 


Sir—  -Spme  time  ago  I  began  to  remodel  our  smelter 
and  this  involved  taking  out  a  small  heater  and  putting 
in  a  larger  one  preparatory  to  erecting  a  larger  furnace 
in  place  0,1  one  of  my  48-in.  diameter  furnaces.  Mean- 
while one  48-in.  furnace  has  been  running  on  hot  blast 
and  the  other  on  cold.  Here  are  two  furnaces  running 
under  exactly  the  same  conditions  as  to  size^  air,  ores 
and  fuel  —  two  48-in.  diameter  water  jackets  almost  ex- 
actly alike.  The  cold-blast  furnace  has  the  advantage  of 
a  more  powerful  blower  and  the  blast  can  be  raised  to 
4  lb.,  while  hot-blast  furnace  gets  less  than  half  that 
pressure  ;  moreover,  the  cold  blast  furnace  is  newer 
and  has  a  better  arrangement  of  tuyeres.  It  seemed  to 
me  that  there  was  a  good  chance  to  compare  hot  and 
cold  blast  results  under  similar  conditions,  with  results 
that  should  be  valuable. 

The  two  furnaces  are  still  running  side  by  side.  I 
send  you,  herewith,  results  for  last  month,  March.  As 
far  as  we  are  concerned  the  hot-blast  furnace  makes 
profits  and  the  cold-blast  comes  perilously  near  making 
losses,  so  great  is  the  difference.  I  can  only  say  that 
during  this  run  it  made  our  American  superintendent 
hustle  to  keep  the  cold-blast  furnace  going,  while  ordi- 
nary Mexican  labor  made  the  hot-blast  furnace  run 
comfortably.  We  had  to  select  both  ores  and  coke  for 
the  cold  blast,  while  the  hot  blast  took  the  leavings 
without  'kicking'  ;  our  superintendent,  at  the  end  of  the 
first  run,  remarked,  "If  we  select  the  ores  and  coke  and 
charge  and  watch  it  very  carefully  and  give  it  plenty  of 
coke,  we  can  get  along,  but  if  we  have  trouble  in  the  fur- 


144 


WALTER  E.  KOCH. 

nace  or  stoppage  of  blast,  it  takes  a  long  time  to  come 
around,  nor  cati  We  run  the  charges  which  the  hot  blast 
furnace  will  take."  On  one  occasion  a  change  of  ore 
during  the  night  made  trouble  in  both  furnaces; 
the  hot-blast  one  was  convalescent  and  working  nor- 
mally in  an  hour,  the  cold  blast  nearly  froze  up,  and  it 
took  almost  a  day  to  come  round.  At  critical  periods 
the  hot  blast  blows  the  furnace  in  and  the  cold  blows  it 
'out.  You  can  put  your  hand  into  the  cold -blast  fur- 
nace and  pull  out  pieces  through  the  tuyeres,  and  there 
are  long  noses  to  them  often,  which  is  never  the  case 
when  using  hot  blast,  indicating  that  the  zone  of  heat- 
ing effect  is  larger  with  the  latter.  Charges  of  ore  which 
will  work  well  with  hot  blast,  and  slags  which  run  fluid 
and  clean  with  hot  blast,  will  not  work  out  or  run  at  all 
with  cold  blast ;  in  fact,  with  cold  blast  you  are  limited 
as  to  charges  and  slags,  and  the  increase  in  coke  re- 
quired is  a  serious  item ;  moreover  the  coke  must  be  se- 
lected and  good.  We  simply  could  not  afford  to  run' 
cold  blast  on  our  low-grade  ores,  and  I  can  see  now 
how  cold  blast  has  spoilt  many  a  good  pyritic  smelting 
proposition,  especially  with  dear,  and  often  dirty,  coke 
and  a  limited  selection  of  ores.  The  oxidizing  power  of 
cold  blast  is  far  less  than  that  of  hot  even  after  increas- 
ing pressure  of  blast/and  there  is  a  great  difference  in 
the  power  of  concentration.  We  get  far  better  and 
quicker  concentration  with  hot  than  with  cold  blast. 
In  every  way  the  advantage  remains  with  the  hot  blast. 
Last  week  we  had  our  first  freeze-up  in  over  two 
years,  and  that  was  on  the  cold-blast  furnace ;  the  hot- 
blast  furnace  went  right  along,  although  it  ran  much 
slower  than  usual  and  the  slag  was  less  fluid  and  the 
production  less.  The  trouble  came,  as  usual,  during-  the 
night,  with  a  change  of  ore  in  the  pile,  and  although  we 
worked  hard,  the  cold-blast  furnace  died  on  our  hands. 
The  hot  blast  also  suffered,  but  the  Mexicans  pulled  it 
straight  in  a  couple  of  hours.  I  cannot  for  the  life  of 

125 


PYRITE    SMELTING. 

me  see  why  any  one  should  advocate  cold  blast ;  it  seems 
to  me  like  'smelter  suicide.'  It  is  certainly  like  fighting 
with  one  hand  tied  behind  your  back.  It  costs  nothing 
beyond  the  first  cost  of  heater,  as  in  our  case  the  furnace 
itself  supplies  the  heat  and  the  heater  is  a  most  efficient 
dust-catcher.  Our  hot  blast  never  runs  over  400°  F.  or 
204°  C,  and  seldom  reaches  that.  It  should  be  called 
"warm  blast." 

The  details  of  our  results  for  the  month  of  March 
were  as  follows : 

MARCH   1  TO    EASTEJR   FIESTA. 

Furnace  A.  Furnace  B. 

Hot  blast.  Cold  blast.  Hot  blast. 

Time  of  run 22  days  16  days  18  days 

Ore  charged  per 

24  hours 41  tons  *31  tons  42  tons 

Coke  charged  per 

cent,  of  charge.  G%  to  6>£  *8#  to  9  5%  to  0 

Coke  charged  per 

ton  of  ore 150lb.  or  7>£%          220  Ib.  or  11%  140  Ib.  or  1% 

Percentage  of  ore 

in  charge 84  81  85 

Concentration up  to  15  to  1,  good    below  10  to  1,  poor    up  to  15  to  1,  good 

Aver,  slag,  45%, 
S1O2,  37%  FeO, 
8%  CaO  and  8% 

less  ore  and  more    previous   run   be- 

flux  fore  change 


*  Coke  and  ore  were  selected  for  cold  blast ;  hot  blast  got  the  leavings  and  did 
not  object. 

Further  details  of  the  furnaces  may  be  useful :  Height 
from  charging  floor  to  base  plate,  84  in. ;  height  from 
charging  floor  to  center  of  tuyeres,  57  in. ;  height  of  cen- 
ter of  tuyeres  above  base-plate,  27  in.  Each  furnace  is 
48  in.  diameter  and  has  twelve  3-5-in.  inclined  tuyeres 
(pitched  downward).  The  heater  for  furnace  B  was 
erected  for  a  42-in.  diameter  furnace  and  is  too  small. 
A  larger  one  is  going  up  now  for  a  126-in.  by  42-in.  fur- 
nace to  displace  B,  which  in  turn  will  displace  A  and 
have  a  larger  heater.  A  has  a  MacDonald  heater,  heat- 
ed by  waste  gases  from  furnace.  Both  furnaces  get 
about  4,000  to  4,500  cu.  ft.  of  air  per  minute,  at  about 
£-lb.  pressure  at  tuyeres,  while  B  can  be  run  up  to  4  Ib. 
at  tuyeres.  B  is  a  newer  and  improved  furnace  in  a  few 

128 


W ALTER  E.  KOCH. 

details,  notably  in  arrangement  of  tuyeres,  and  with  hot 
blast  can  beat  A  by  a  good  margin. 

I  do  not  consider  our  coke  consumption  as  low  as  it 
should  be,  and  will  be,  I  hope,  later  on.  It  should  be 
nearer  5  per  cent  than  7  per  cent  per  ton  of  ore,  or  4  to 
6  per  cent  on  the  total  charge,  and  10  per  cent  is  quite 
disgraceful  in  any  furnace  matting  copper  ores. 

If  loss  of  time,  output,  temper  and  sleep  could  be  put 
against  furnace  B  on  cold  blast  it  would  be  a  large  ac- 
count. No  more  cold  blast  for  me,  although  I  am  still 
running  B  on  cold  blast  till  the  new  furnace  is  ready  to 
erect ;  while  we  get  tonnage  arid  keep  our  men  together, 
it  cuts  into  profits ;  the  cost  of  coke  being  over  $20  gold 
per  ton  at  smelter.  Furnace  B  uses  over  50  per  cent 
more  coke  on  cold  than  on  hot  blast,  with  smaller 
charges  of  the  same  ores. 

WALTER  E.  KOCH. 
Santa  Maria  del  Oro,  April  29,  1904. 


127 


CONTRIBUTION  BY  W.  H.  FREELAND. 

The  Editor : 

Sir— In  response  to  your  request  to  supplement  my 
contribution  upon  this  subject,  I  take  pleasure  in  stat- 
ing that  the  experimental  work  of  the  Ducktown  Sul- 
phur, Copper  &  Iron  Company,  Ltd.,  carried  on  at 
intervals,  for  several  years  past,  was  concluded  by  the 
test  campaign,  the  detailed  data  of  which  appeared  in 
your  issue  of  May  2,  1903.  Following  that,  the  last  of 
its  stock  of  roasted  ore  was  cleaned  up  towards  the  end 
of  September,  1903,  and  since  then  its  whole  furnace 
plant  has  run  exclusively  and  constantly  on  raw  ore. 
Almost  70,000  tons  of  raw  ore  have  been  smelted  in  the 
past  seven  months,  with  less  trouble  and  interruption 
than  records  show  for  any  similar  period  and  tonnage 
on  roasted  ore. 

The  conditions  and  results  of  the  commercial  practice 
tally  so  closely  with  those  of  the  experimental  campaign 
as  to  confirm  and  verify  (literally)  the  data  already  pub- 
lished. The  only  important  modifications  of  those  data 
are :  A  very  material  gain  in  furnace's  capacity ;  the  use 
of  slag  on  the  charge  has  been  entirely  discarded ;  and  a 
heavier  blast  is  used. 

Furnace  Capacity. — Referring  to  this  feature  in  my 
original  article,  it  will  be  noticed  that  a  loss  of  efficiency 
of  48  per  cent  was  shown  on  furnace's  performance  on 
raw  ore,  as  compared  with  roasted  ore.  The  same 
furnace  is  now  averaging  no  tons  of  raw  ore  per  day; 
deducting  the  time  necessary  to  re-concentrate  the 
matte  from  'first  operation'  gives  an  average  capacity 
(including  both  operations)  of  96  tons  raw  ore  per  day, 
or  a  loss  of  efficiency  of  only  16.5  per  cent  instead  of  the 
48  per  cent  originally  quoted. 

123 


W.  H,  FREELAND. 

Preparations  are  being1  made  to  further  increase  the 
blast,  which,  when  completed,  will  still  further  increase 
the  furnace  tonnage. 

Opinions  of  the  Process. — Considerable  interest  in  the 
Ducktown  Sulphur,  Copper  &  Iron  Company's  practice 
having  been  expressed  by  others,  the  following  may  be 
quoted  from  the  Boston  News  Bureau  of  November  16, 
1903,  as  Mr.  J.  Parke  Channing  has  had  numerous 
opportunities  of  seeing  and  studying  the  operations : 
"According  to  President  Channing,  of  the  Tennessee 
Copper  Company,  Mr.  Freeland  has  admirably  suc- 
ceeded in  these  experiments,  and  his  plant  is  now  run- 
ning entirely  on  raw  ore,  and  making  both  a  technical 
and  commercial  success.  It  is  solely  as  a  result  of  his 
successful  experiments  that  the  Tennessee  Copper  Com- 
pany decided  to  adopt  the  same  methods.'' 

Comparative  Economy  of  the  Process. — The  plant  and 
equipment  of  the  Ducktown  Sulphur,  Copper  &  Iron 
Company  is  not  of  modern  design,  yet  under  its  con- 
ditions, a  reduction  of  3.oi8c.  in  the  cost  per  pound  of 
copper  is  effected  by  raw  sulphide  smelting.  The  writer 
is  of  the  opinion  that  an  up-to-date  plant  should  make 
an  even  better  showing,  and  it  is  to  be  hoped  that  our 
immediate  neighbors,  the  Tennessee  Copper  Company, 
with  their  admirable  plant,  will  confirm  that  opinion  in 
the  near  future,  as  that  company  is  now  making  prepa- 
rations to  adopt  the  same  methods. 

W.  H.  FREELAND. 
Isabella,  Tenn.,  May  2,  1904. 


129 


CONTRIBUTION  BY  AMADO  BUEN. 

The  Editor : 

Sir — In  reading-  the  various  articles  on  matte  smelt- 
ing I  notice  that  though  hot  blast  is  generally  conceded 
to  increase  the  capacity  and  to  give  cleaner  slags  and 
better  conditions  in  general,  the  stoves  are  of  low  effi- 
ciency and  troublesome  to  keep  in  repair.  As  the  fur- 
nace gases  cannot  be  used  for  fuel,  brick  stoves  seem 
not  to  have  been  tried  at  all,  as  they  need  a  gaseous  fuel. 
It  appears,  however,  that  for  conditions  like  southern 
Arizona,  where  petroleum  is  used  to  heat  boilers  instead 
of  coal,  petroleum  might  just  as  easily  be  used  to  heat  a 
brick  stove,  when  all  the  trouble  coming  from  cast-iron 
stoves  would  disappear,  and  a  plant  might  in  this  way 
largely  increase  its  capacity  and  decrease  its  fuel  con- 
sumption. From  what  I  have  observed  at  smelters  in 
southern  Arizona,  success  in  running  a  furnace  with  a 
top  fire  depends  almost  entirely  on  judgment  in  feeding 
the  furnace.  I  have  seen  at  one  plant  how  the  blow- 
holes, that  always  form  with  high-pressure  blast,  are 
fed  with  slag  by  hand,  with  the  intention  of  keeping  the 
furnace  open,  and  the  result  is  that  by  feeding  an  easily 
fusible  material  into  that  part  of  the  furnace  which  is 
open,  the  rest  is  chilled  and  the  furnace  is  always  in  a 
bad  condition  and  full  of  crusts.  Also,  at  the  same  plant, 
the  weight  of  the  charges,  ore  and  coke,  has  been  de- 
creased, with  the  result  that  the  coke  does  not  get  a  suf- 
ficiently thick  cover  to  keep  it  from  burning  out  before 
it  reaches  the  fusion  zone.  As  the  plant  is  new  and  the 
method  of  charging  is  directly  from  the  cars,  which 
dump  sideways  into  the  furnace,  this  arrangement  has 
been  blamed  for  the  unsatisfactory  running.  At  a  neigh- 

130 


AM  ADO  BUEN. 

boring  plant,  however,  though  the  material  is  brought 
up  in  big  two-wheel  barrows  by  hand,  the  dumping  into 
the  furnace  is  exactly  the  same,  almost  no  hand-shovel- 
ing being  done.  Only  the  charges  are  larger,  and  special 
care  is  taken  to  cover  the  coke  up  immediately  with  a 
large  amount  of  ore,  and  to  put  ore  and  not  slag  on  top 
of  the  blow-holes,  while  the  slag  is  put  to  those  places 
which  show  the  least  heat,  and  the  furnace  keeps  in 
good  condition  all  over. 

AMADO  BUEN. 
Douglas,  Arizona,  May  21,  1904. 


181 


PYRITE  SMELTING.— A  REVIEW. 

By  EDWARD   D.   PETERS. 

INTRODUCTORY. 

At  the  request  of  the  Editor,  I  have  undertaken  to 
review  and  comment  upon  a  series  of  papers  on  the 
subject  of  pyrite  smelting  which  have  appeared  in  the 
columns  of  The  Engineering  and  Mining  Journal  be- 
tween October  10,  1903,  and  the  present  time. 

Pyrite  smelting  is  a  process  of  very  recent  develop- 
ment, and  its  published  literature  is  meagre.  A  large 
proportion  of  the  metallurgists  best  qualified  to  write 
authoritatively  upon  the  subject,  are  actively  engaged  in 
practising  and  developing  it,  and  have  no  time  to  write 
treatises.  Messrs.  W.  L.  Austin,  F.  R.  Carpenter  and 
Herbert  Lang  had  previously  given  us  much  valuable 
information  as  to  the  results  obtained  in  their  own  prac- 
tice; but  there  were  many  other  metallurgists  doing 
highly  original  and  successful  work  in  this  field,  from 
whom  it  was  deemed  desirable  to  hear.  The  editor  of 
the  Journal,  therefore,  sent  out  last  autumn  a  series  of 
ten  questions  to  a  considerable  number  of  the  metal- 
lurgists of  the  world  who  are,  or  have  been,  engaged 
in  this  branch  of  the  art.  The  replies  to  these  questions 
constitute  a  body  of  information  on  the  subject  of  pyrite 
smelting  that  I  believe  to  be  unique  in  the  metallurgy 
of  copper,  both  for  its  comparative  unanimity  of 
opinion,  and  for  the  authority  of  the  sources  from  which 
it  comes. 

It  is  the  object  of  this  review  to  present,  in  a  con- 
cise and  graphic  form,  the  results  and  opinions  reached 
by  these  authors;  to  draw  general  deductions  from 

132 


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smelted 
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amounts  of  Zn 


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coke  is  cheap.  Presence 
of  ZnSand  of  fine  would 
also  affect  decision. 


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»      % 
<t 


ATI, 
om 
sof  Pb 
o  mixe 
orm 
and  mat 
heat. 


An 
free 
tities 
be  so 
to  fo 


My  later  experience  is 
altogether  favorable  to 
the  use  of  the  hot  blast. 
It  saves  fuel  and  in- 
creases capacity. 


Varies  with  conditions. 
Hot  blast  may  save  fc>  to 
%ofthecoke.  Smelting 
heavy  sulphides  with 
cold  blast  usually  means 
little  coke  and  a  low  ratio 
of  concentration. 


ii 


s- 


®+Z 

ss 


00        O  0 


gl'fsl 

IS! 
fKij 

u  3  oJ  03  OD*J  ^ 
c  qaS5-< 


S  0 

M     ®   *" 


Competitive  methods, 
or  combination  of  meth- 
ods, showing  greater 
economy,  governed  to  a 
great  extent  by  fines, 
ZnS,  and  cost  of  coke. 


Less  costly  plant. 
No  roasting. 
Rapidity. 
Silicious  and  cl 


!!!! 
Hll 


«  0 


!Hi 

°SSB 

a  wc-o 

Uli 

Mlf 

^la 

"1SS 


dltloni 
no 


dlt 
has 
l. 


Co 
ons 
mel 
ear 
ble 


Where 
uitable, 
essful  r 


Irit"! 
"ISalS 


OOM.C]  ^ 

"lit 


02  ° 


2  3 

Z     3: 


E.  D.  PETERS. 

them,  so  far  as  seems  justifiable ;  and,  incidentally,  to 
comment  on  and  discuss  such  points  in  them  as  seem  to 
invite  further  consideration.  Ten  of  the  replies  answer 
all,  or  nearly  all,  of  the  questions  categorically,  and  thus 
lend  themselves  to  the  construction  of  a  table,  where  a 
bird's-eye  view  may  be  had  of  the  opinion  of  each  metal- 
lurgist on  each  separate  question.  It  has  been  difficult 
to  express  in  a  few  words  an  opinion  that  may,  perhaps, 
have  occupied  an  entire  column  in  the  original  reply, 
and  I  must  ask  the  indulgence  of  the  authors. 

The  results  of  this  tabulation  are  striking,  and  it  is 
interesting  to  note  how  little  difference  of  opinion  there 
is  in  the  replies.  Indeed,  where  differences  of  opinion 
exist  at  all,  it  is  nearly  always  due  to  the  fact  that  some 
of  the  individual  questions  cover  so  much  ground  that 
they  admit  of  a  good  deal  of  variation  in  the  answer, 
without  there  being  any  actual  conflict.  It  is  simply 
that  they  have  been  answered  from  a  different  stand- 
point, and  that  each  author  tends,  naturally,  to  base  his 
reply  upon  the  particular  class  of  ore  that  he  is  work- 
ing, and  upon  which  much  of  his  experience  is  based ; 
for  pyrite  smelting,  in  its  modern  form,  is  of  too  recent 
origin  to  admit  of  a  very  wide  or  varied  experience  on 
the  part  of  any  one  person. 

Thus,  as  a  typical  instance  where  conditions  compel 
two  differing  answers  to  the  same  question :  Mr.  G.  F. 
Beardsley  has  for  years  been  smelting  the  unusually 
heavy  pyrite  ores  of  the  Mt.  Lyell  mine,  in  Tasmania, 
using  enormous  furnaces,  and  a  high  blast-pressure, 
and,  owing  to  the  great  preponderance  of  basic,  ferrug- 
inous ores,  has  been  compelled  to  produce  a  slag  as 
high  in  iron  and  as  low  in  silica  as  was  compatible  with 
the  desired  ratio  of  concentration.  Consequently,  his 
replies  to  certain  of  Mr.  Rickard's  questions  must, 
necessarily,  be  widely  different  from  Mr.  S.  E.  Brether- 
ton's,  who,  at  his  smelter  at  Val  Verde,  Arizona,  is 
almost  always  short  of  pyritous  material;  whose  coke 

137 


PYRITE    SMELTING. 

costs  $13  per  ton;  whose  profit  arises  almost  entirely 
from  the  srnelting-tariff  on  silicious-gold  and  silver  ores, 
containing  more  or  less  arsenic,  antimony,  lead  and 
zinc,  all  of  which  he  has  to  completely  remove  in  the 
pyritic  fusion,  so  that  his  matte  may  not  be  penalized  by 
the  refiners  for  these  substances  ;  and  who  has  no  copper 
in  his  charge,  excepting  the  little  that  he  is  forced  to 
add  to  collect  the  precious  metals,  and  which  he  has 
to  bring  by  rail  from  a  distance  of  some  500  miles. 

Here  are  certainly  conditions  as  diametrically  op- 
posed to  each  other  as  one  can  well  imagine;  yet  a 
careful  perusal  of  the  two  vertical  columns  of  answers 
in  the  table,  headed  by  the  names  of  Beardsley  and 
Bretherton,  will  show  that  these  two  highly  experienced 
metallurgists  have  arrived  at  conclusions  that  are  almost 
identically  the  same  in  nearly  every  respect.  There  are 
some  points  in  each  set  of  answers  that  are  not  touched 
upon  in  the  other.  But  there  is  no  common  point  on 
which  the  two  differ  materially.  In  no  instance  do  their 
replies  contradict  each  other;  they  merely  supplement 
each  other.  This  same  unanimity  of  conclusions  will 
be  found  to  prevail  pretty  generally  throughout  the  en- 
tire one  hundred  answers. 

A  similar  agreement  in  experience  and  deductions 
will  be  found  in  the  letters  of  Messrs.  Ingalls,  Wein- 
berg,  Godshall,  Heywood,  Read  and  others,  which  form 
a  part  of  this  same  discussion,  and  of  which  I  shall 
equally  avail  myself  in  this  review,  although  it  was  im- 
possible for  me  to  include  them  in  the  table  without 
taking  greater  liberties  with  the  text  than  would  have 
been  justifiable. 

When  a  dozen  or  more  practical  and  experienced 
metallurgists  agree  upon  a  technical  point,  we  may  feel 
safe  in  accepting  it  as  a  fact — at  least,  until  it  is  modi- 
fied by  new  evidence.  In  these  replies,  there  is  such 
an  agreement  to  a  very  remarkable  extent,  and  we  have 
here  the  material  for  the  construction  of  a  more  solid 

188 


E.  D.  PETERS. 

basis  of  information  in  regard  to  pyrite  smelting  than 
we  have  hitherto  possessed,  though  many  of  the  views 
enunciated  in  these  letters  have  been  foreshadowed,  and, 
in  some  instances,  distinctly  stated  from  time  to  time 
in  articles  by  Messrs.  W.  L.  Austin,  Carpenter,  Lang 
and  others. 

i.    TYPES  OF  ORE  SUITED  TO  THE  PROCESS. 

In  the  series  of  questions  sent  out  by  The  Engineering 
and  Mining  Journal,  the  first  in  order  is :  I.  What  types 
of  ore  are  suited  to  the  process  ?  So  much  of  the  same 
ground  is  also  covered  by  the  ninth  question,  "What  are 
the  limitations  of  the  process  ?"  that  the  two  can  be  ad- 
vantageously considered  together. 

The  fact  that  the  questions  refer  to  pyrite  smelting 
implies  the  presence  of  a  certain  proportion  of  sulphides 
in  the  charge ;  else  it  would  not  be  pyrite  smelting.  Con- 
sequently there  is  little  variation  in  the  replies  to  these 
two  questions. 

Pre-supposing  the  presence  of  sulphides,  the  general, 
or  composite,  answer  might  be :  "Any  mixture  of  gold, 
silver,  or  copper  ores  that  will  yield  a  fusible,  and  rather 
silicious,  slag."  Certain  of  the  replies  indicate  some 
limitations,  and  it  is  to  these  that  our  attention  must  be 
mainly  directed. 

The  presence  of  a  considerable  proportion  of  fines 
in  the  charge  is  mentioned  by  several  of  the  contributors 
as  being  objectionable ;  as,  indeed,  it  certainly  is  in  ordi- 
nary blast-furnace  smelting.  In  pyrite  smelting  it  may 
be  particularly  dangerous  in  cases  where  the  silicious 
portion  of  the  charge  is  comparatively  coarse,  while 
the  raw  sulphides  exist  in  the  shape  of  fines.  Under 
such  circumstances,  the  sulphide  fine  will  trickle  down 
through  the  interstices  of  the  charge,  and,  owing  to 
its  fusibility,  melt  into  matte  without  remaining  long 

139 


PYRITE    SMELTING. 

enough  in  the  oxidizing  atmosphere  above  the  tuyeres. 
This  circumstance  produces  three  serious  evils : 

1.  An  excessive  formation  of  low-grade  matte. 

2.  A  dearth  of  iron  with  which  to  flux  the  silica. 

3.  A  waste  of  fuel ;  the  sulphides  going  into  the  matte 
instead  of  burning  so  as  to  supply  much  of  the  heat 
required  for  smelting  the  ore. 

There  are  two  obvious  remedies  for  this  trouble,  both 
of  which  I  have,  at  various  times,  employed,  or  seen  em- 
ployed. One  is  the  wrong  one;  the  other,  the  right 
one.  The  wrong  remedy  is  to  attempt  to  supply  the  de- 
ficiency in  heat  by  adding  more  coke.  This  is  the  step 
usually  first  taken  by  men  who  are  inexperienced,  and  is 
quickly  fatal.  The  trouble  that  already  exists  in  the 
furnace  is,  that  not  enough  pyrite  is  being  oxidized  to 
furnish  ferrous  oxide  with  which  to  flux  the  silica.  The 
addition  of  more  coke  fills  the  furnace  shaft  with  power- 
fully reducing  gases,  and  prevents  the  oxidation  of  even 
that  small  proportion  of  pyrite  which  was  being  changed 
into  ferrous  oxide.  The  result  is,  of  course,  that,  under 
the  new  conditions,  even  this  little  oxidation  ceases, 
practically  all  of  the  sulphides  go  into  the  matte,  and 
the  slag  becomes  too  silicious  to  melt  at  all. 

The  right  remedy  is  to  change  the  physical  condition 
of  the  sulphide  fine,  so  that  it  shall  not  trickle  down 
through  the  interstices  of  the  charge.  This  can  be  ac- 
complished in  two  different  ways,  either  of  which  is 
reasonable,  though  only  local  conditions  can  determine 
which  is  the  more  economical. 

1.  Mixing    the    fine    with    lime,    and    briquetting    it 
under  pressure,  which  is  perfectly  feasible  for  raw  sul- 
phides. 

2.  Fusing  into  an  iron  matte  in  a  large  reverberatory 
furnace.     The  capacity  of  such  a  furnace  running  on 
raw  sulphide  is  enormous,  while  the  fuel  consumption 
is  very  small,  and,  as  the  main  result  of  this  operation  is 

140 


E.  D.  PETERS. 

simply  to  change  the  FeS2  into  FeS,  there  is  compara- 
tively little  loss  in  heat-producing  constituents.  The 
weight  of  the  raw  sulphide  is  considerably  reduced,  and 
the  resulting  iron  matte  forms  a  valuable  fuel  and  flux 
in  lump  form.  The  fact  that  it  makes  no  flue-dust, 
when  added  to  the  blast  furnace  charge,  also  tends  to 
reduce  the  cost  of  this  reverberatory  fusion. 

A  large  percentage  of  zinc-blende  in  the  charge  Is 
referred  to  by  several  of  the  contributors  as  being  par- 
ticularly objectionable  in  pyrite  smelting.  As  the  sixth 
question  deals  exclusively  with  this  unwelcome  mineral, 
I  will  omit  all  discussion  of  it  under  the  present  head- 
ing. 

None  of  the  replies  object  seriously  to  the  presence 
of  lead  sulphide,  except  to  point  out  that  it  is  wasted  in 
the  pyritic  furnace,  the  lead  being  mostly  volatilized  or 
slagged. 

Mr.  L.  D.  Godshall  calls  attention  to  two  conditions 
where  the  ordinary  smelting  of  roasted  ore  might  prove 
more  advantageous  than  pyrite  smelting.  These  are: 
(i)  Where  the  smelter  will  not,  in  a  single  fusion,  give 
the  desired  degree  of  concentration;  and  (2)  where 
there  is  a  large  amount  of  zinc-blende  in  the  charge. 

To  these  two  conditions  I  will  add  still  another:  (3) 
Where  sufficient  silicious  ore  cannot  be  obtained,  and 
it  becomes  necessary  to  smelt  with  a  rather  basic  slag. 

Mr.  Godshall's  first  condition  really  includes  mine, 
and  I  have  only  made  this  apparently  superfluous  addi- 
tion in  order  to  bring  out  separately  and  emphatically 
what  I  think  may  be  called  the  most  important  maxim 
in  the  art  of  pyrite  smelting;  namely,  that,  other  things 
being  equal,  the  degree  of  concentration  increases  with  the 
percentage  of  silica  in  the  charge.  (This  point  will  be 
taken  up  when  discussing  the  seventh  question.)  Con- 
sequently, if  we  have  heavy  sulphide  ores,  and  cannot 
profitably  obtain  sufficient  quartz  (and  it  must  be,  at 
least  in  part,  free  silica,  and  not  feldspar  or  clay  or  gar- 

141 


PYRITE  SMELTING. 

net)  to  form  a  tolerable  silicious  slag ;  and  if  these  ores 
are  not  rich  enough  in  copper  to  give  us,  even  with 
our  probable  low  rate  of  concentration,  a  45  to  50  per 
cent  matte  on  the  first  smelting,  we  shall  be  con- 
fronted with  the  necessity  of  putting  this  matte  through 
a  second  pyritic  fusion,  in  order  to  bring  it  up  to  a  suit- 
able grade  for  converting. 

A  concentrating  smelting  of  the  raw  matte  is  not  at 
all  a  serious  matter  where  our  ratio  of  concentration 
has  been  high ;  because,  under  such  circumstances,  the 
cost  per  ton  of  original  ore  will  be  very  small.  Indeed, 
in  a  silicious  district  where  there  is  a  high  smelting 
tariff  on  quartzose  ores,  this  cost  may  be  in  great  part 
offset  by  the  profit  obtained  from  the  silicious  ores 
that  we  smelt  in  connection  with  the  raw  matte,  and 
which  it  is  absolutely  necessary  to  smelt  with  it  unless 
we  desire  to  see  it  come  out  of  the  furnace  in  pretty 
much  the  same  condition  as  when  it  went  in. 

On  the  other  hand,  when  the  ratio  of  concentration 
on  the  first  smelting  has  been  low,  this  second  fusion 
of  the  raw  matte  constitutes  a  serious  charge  against 
each  ton  of  the  original  ore,  and  it  is  in  these  very  cases 
that  we  also  usually  fail  to  obtain  any  profit  from  the 
silicious  ores  that  it  is  necessary  to  use  in  the  concen- 
tration-smelting of  the  matte.  This  arises  from  the 
very  simple  reason  that,  if  it  had  been  a  district  where 
there  was  a  good  smelting  profit  on  silicious  ores,  we 
should  have  used  enough  of  them  in  the  original  ore 
smelting  to  have  formed  a  silicious  slag  that  would 
have  given  us  a  satisfactory  rate  of  concentration  in  the 
first  place. 

I  therefore  agree  entirely  with  Mr.  Godshall  that 
there  may  be  certain  conditions  where  sulphide  ores  can 
be  more  economically  treated  by  roasting  and  smelting 
than  by  pyrite  smelting.  I  believe,  however,  that  these 
conditions  are  mainly  limited  to  districts  where  silicious 
ores  are  scarce. 

142 


E.  D.  PETERS. 

Mr.  Godshall's  second  limiting  condition  refers  to 
ores  containing  too  much  zinc-blende.  It  is  pointed 
out  both  by  Mr.  Godshall  and  Mr.  Ingalls  that  zinc- 
blende  is  much  more  easily  smelted  if  it  has  been  oxid- 
ized outside  of  the  blast  furnace,  than  if  both  oxidizing 
and  smelting  are  conducted  in  the  same  operation 
within  the  furnace.  No  doubt  all  metallurgists  will 
agree  with  this  statement,  and  the  main  point  to  deter- 
mine for  each  individual  case  would  be,  at  just  what 
percentage  of  blende  it  would  be  more  advantageous  to 
give  up  pyrite  smelting  and  submit  the  ore  to  a  pre- 
liminary roasting.  A  fuller  discussion  of  this  matter 
will  be  deferred  until  we  reach  the  sixth  question,  which 
deals  exclusively  with  zinc. 

It  seems  to  me  that,  in  replying  to  the  first  question, 
Mr.  Lang  goes  to  the  root  of  the  matter.  He  says  he 
should  like  to  modify  the  question  so  that  it  might  read : 
''What  kind  of  ore  mixture  is  best  suited  to  the  process  ? 
One  ore  is  as  well  suited  to  pyrite  smelting  as  another, 
provided  its  values  are  in  gold,  silver,  or  copper,  and 
that  it  be  smelted  with  other  ores  and  fluxes  that  make 
up  its  deficiencies  as  a  builder  of  slag  and  matte,  and  a 
furnisher  of  heat." 

In  speaking  of  the  necessity  of  always  having  enough 
silica  (in  excess  of  that  needed  to  form  a  bi-silicate  of 
lime  and  a  singulo-silicate  of  iron)  to  decompose  the 
iron  sulphides,  and  thus  effect  the  required  degree  of 
concentration,  Mr.  Lang  emphasizes  the  important 
point  that  the  native  silicate  minerals,  that  we  find  so 
commonly  in  ores,  probably  do  not  exert  this  decom- 
posing influence  upon  the  sulphides ;  but  that  free 
silica  is  required  for  this  purpose.  That,  therefore, 
these  native  silicates — such  as  garnet,  hornblende,  and 
the  alumina  silicates — may,  of  course,  be  smelted  inci- 
dentally to  the  process,  and  will  aid  in  rendering  the  slag 
silicious,  but  do  not  directly  assist  in  the  decomposition 
of  the  sulphides. 

143 


PYRITE    SMELTING. 

I  will  mention  another  class  of  ores  that  seems  to  be 
peculiarly  adapted  to  this  process ;  not  because  the 
pyrite  smelter  has  any  particular  affection  for  them,  but 
because  they  are  very  much  less  objectionable  in  the 
pyritic  furnace  than  in  the  ordinary  blast  furnace  with 
coke.  I  refer  to  ores  containing  a  large  proportion  of 
barite,  which  in  ordinary  blast-furnace  work  forms  an 
undue  amount  of  matte  of  low  specific  gravity,  and  tends 
to  reduce  greatly  the  capacity  of  the  furnace,  and  to  in- 
crease the  losses  in  the  slag.  In  the  pyritic  furnace, 
when  using  a  reasonably  acid  slag,  barite  is  mostly  de- 
composed, the  BaO  entering  the  slag  as  a  valuable  base, 
whilst  the  sulphur  trioxide  escapes  through  the  stack. 

It  seems  to  me  that  we  may  justly  draw  the  following 
deductions  from  the  replies  to  Questions  I  and  9:  All 
ores,  or  mixtures  of  ores,  containing  copper,  gold  or 
silver  are  suitable  for  pyrite  smelting,  provided  they 
contain  the  constituents  for  the  formation  of  a  suitable 
matte  and  slag,  and  do  not  contain  too  large  a  propor- 
tion of  zinc-blende.  (See  also  Question  6.) 

The  conditions  where  roasting  and  smelting  might  be 
more  economical  than  straight  pyrite  smelting  are : 

1.  With  heavy  pyrite,  and  insufficient  profitable  sili- 
cious  ores. 

2.  Where  too  much  zinc-blende  is  present. 

2.     USE  OF  HEATED  BLAST. 

Nine  of  the  ten  tabulated  replies  to  the  question,  'Is 
hot  blast  advisable?'  are  in  the  affirmative.  Five  of 
them  are  emphatic.  The  remaining  four  speak  of  hot 
blast  as  advantageous  rather  than  essential.  The  tenth 
reply  regards  it  as  more  or  less  advantageous,  but  at- 
taches much  less  importance  to  it  than  do  the  others. 

The  trouble  with  this  question  is  that  it  covers  too 
much  ground.  Where  there  is  a  great  abundance  of 
iron  sulphides,  and  a  consequent  ample  generation  of 

144 


E.  D.  PETERS. 

heat  from  their  oxidation,  the  advantages  of  a  hot  blast 
are,  of  course,  much  less  apparent  than  where  there  is 
an  earthy  and  silicious  charge,  with  a  moderate  amount 
of  pyrite,  and  yet  where  a  high  degree  of  concentra- 
tion is  required.  (This  condition  occurs  most  often  in 
the  dry  smelting  of  gold  and  silver  ores,  and  where  even 
unprofitable  copper  is  added  to  collect  the  precious 
metals.) 

In  the  former  case,  there  is  an  ample  excess  of  heat 
to  warm  a  cold  blast  of  air  up  to  the  temperature  of 
the  smelting  zone,  and  the  harder  one  blows,  the  more 
heat  there  will  be,  for  the  more  rapidly  will  the  pyrite 
be  burned ;  the  rate  of  concentration  being-  mainly  con- 
trolled by  the  amount  of  silica  added.  In  the  latter 
case,  however,  the  conditions  are  quite  different.  The 
moderate  quantity  of  pyrite  in  the  charge  does  not  fur- 
nish sufficient  heat  for  fusion;  and  yet  the  3  or  4  per 
cent  of  coke  that  is  being  used  to  make  up  the  defi- 
ciency cannot  be  increased,  or  some  of  the  FeS  will  go 
into  the  matte  instead  of  being  oxidized;  the  ratio  of 
concentration  will  suffer,  and  the  slag  will  at  once  be- 
come too  silicious  from  the  loss  of  its  FeO,  which  has 
gone  into  the  matte  as  FeS.  Thus  the  metallurgist  is 
"between  the  devil  and  the  deep  sea."  If  he  does  not 
add  coke,  his  furnace  will  chill  for  want  of  heat.  If  he 
does  add  coke,  his  matte  will  be  low  grade,  and  his 
furnace  will  chill  from  too  silicious  a  slag.  It  is  in  such 
cases  as  this,  where  the  furnace  is  continuously  on  the 
ragged  edge  of  freezing-up,  that  the  hot,  or  even  warm, 
blast  becomes  not  only  advantageous,  but  indispen- 
sable. 

Dr.  Carpenter  conies  the  nearest  of  any  one  to  deny- 
ing the  economic  advantage  of  hot  air.  He  has  had 
great  experience,  and  every  one  will  attach  much 
weight  to  his  opinion.  After  stating  that  "It  reduces 
fuel  to  the  extent  of  heat  so  added,  but  that  the  best  hot- 
air  stove  is  a  very  wasteful  machine  when  heated  with 

145 


PYRITE  SMELTING. 

extraneous  fuel,"  he  adds  that  he  "never  has  found  the 
magic  in  mere  hot  air  that  others  have  professed  to 
find."  This  is  not  easy  to  reconcile  with  his  opinion 
expressed  in  Vol.  X  of  The  Mineral  Industry,  page  698, 
that  "At  Golden,  Colorado,  the  Deadwood  practice  was 
materially  improved  by  the  addition  of  hot  air,  without 
which  pyritic  smelting  should  not  be  attempted." 

Mr.  Fulton  says  that  he  cannot  speak  from  experi- 
ence, but  that  he  believes  that  the  use  of  a  hot  blast 
notably  increases  the  oxidizing  effect  of  the  smelting, 
and,  consequently,  improves  the  degree  of  concentra- 
tion. 

Mr.  Mathewson  also  refers  to  the  effect  of  a  hot  blast 
in  improving  the  degree  of  concentration,  but,  in  a  pri- 
vate letter  to  myself,  desires  to  limit  this  statement  to 
cases  where  there  is  not  a  high  percentage  of  sulphur 
in  the  charge,  and  where  the  ore  column  in  the  fur- 
nace is  lowered.  The  wonderfully  rapid  smelting  that 
Mr.  Mathewson  is  now  doing  at  Anaconda  is  of  just 
the  kind  that  does  not  require  a  hot  blast,  there  being  a 
large  proportion  of  heavy  sulphide  ore  in  the  charge, 
and  the  ratio  of  concentration  being  unusually  low, 
owing  to  the  high  percentage  of  copper  in  the  material 
smelted. 

Mr.  Nutting  believes  that  "metallurgically,  the  hot 
blast  is  always  advantageous."  He  doubts,  however, 
whether  it  is  always  economically  profitable  where  coke 
is  comparatively  cheap.  Here,  again,  we  have  con- 
ditions where  a  hot  blast  is  not  indispensable.  At  the 
Bingham  smelter,  they  have  rather  cheap  coke,  ample 
sulphide  ores,  and  a  moderate  ratio  of  concentration. 

Mr.  Beardsley  speaks  strongly  in  favor  of  hot  blast 
where  it  is  necessary  to  make  a  silicious  slag,  and 
equally  strongly  regarding  the  unsatisfactory  duty  of 
U-pipe  stoves.  It  has  been  found  possible  at  Mt.  Lyell 
to  do  without  them  at  all,  and,  by  heightening  the  ore 
column,  and  greatly  increasing  the  blast,  the  furnaces 

146 


E.  D.  PETERS. 

are  putting  through  a  very  large  tonnage,  and  still  oxid- 
izing the  sulphides  sufficiently  to  maintain  a  fair  degree 
of  concentration.  Here  is  a  typical  case  of  smelting  a 
massive  pyrite  ore,  with  the  addition  of  the  least 
amount  of  silica  necessary  to  produce  a  suitable  slag. 
The  charge  is  highly  fusible,  and  contains  an  unusual 
proportion  of  heat-producing  constituents. 

The  foregoing  are  the  types  of  pyrite  smelting  that 
obtain  the  least  advantage  from  the  use  of  the  heated 
blast. 

Mr.  L.  S.  Austin  considers  a  hot,  or  even  warm,  blast 
of  assistance  in  raw  smelting,  but  emphasizes  its  value 
particularly  in  smelting  a  very  silicious,  or  infusible, 
charge.  He  also  refers  to  the  difficulty  so  often  experi- 
enced with  the  apparatus  for  heating  the  blast. 

Mr.  Bretherton  speaks  emphatically  as  to  the  neces- 
sity of  a  heated  blast  in  pyrite  smelting.  I  have  already 
alluded  to  the  conditions  under  which  he  is  working, 
which  are  diametrically  opposite  to  those  of  Beardsley 
or  Nutting  or  Mathewson,  and  which,  I  am  quite  con- 
vinced from  personal  observation,  render  a  heated  blast 
indispensable  to  his  existence  at  Val  Verde  as  a  success- 
ful smelter.  He  seems  to  have  no  difficulty  with  the 
stove  of  his  invention,  which,  on  my  late  visit  to  Val 
Verde,  was  consuming,  per  24  hours,  2.5  cords  of  old 
railway  ties  to  heat  the  blast  for  his  i6o-ton  furnace. 

Mr.  Koch,  of  La  Lustre  smelter  at  Sta.  Maria  del 
Oro,  speaks  strongly  in  regard  to  the  advantages  of 
the  hot  blast.  He  says :  "A  warm  blast  of  200°  C.  is  a 
sine  qua  non  with  us  ;  it  spelled  success ;  cold  blast  meant 
failure."  I  can  well  understand  that,  in  smelting  the 
silicious  ores  of  the  Magistral  vein  with  7  per  cent  coke, 
and  making  a  concentration  of  1.5  into  i,  Mr.  Koch 
may,  indeed,  depend  upon  the  heated  blast.  It  is  a  typi- 
cal case  for  its  employment.  Since  Mr.  Koch's  first 

147 


PYRITE    SMELTING. 

communication  on  the  subject  he  has  carried  out  a  test1 
between  two  furnaces  operating  under  like  conditions 
except  as  to  blast,  and  the  results  thoroughly  confirm 
the  opinion  previously  expressed  by  him. 

Mr.  Lloyd  also  speaks  strongly  in  favor  of  heated 
blast. 

Mr.  Herbert  Lang,  who  is  credited  with  being  the 
first  person  to  demonstrate  that  pyrite  smelting  without 
a  heated  blast  was  possible  at  all,  throws  the  weight  of 
his  experience  entirely  on  the  side  of  the  hot  blast.  He 
says :  "I  believe  that  it  invariably  decreases  the  cost  of 
treating  the  ore.  ...  I.  It  saves  fuel.  2.  It  makes  the 
furnace  drive  faster  and  smelt  more  in  a  day."  He  also 
adds :  "The  furnaces  I  have  known  run  faster  with  hot 
blast  than  with  cold."  He  speaks  strongly  of  the  de- 
fects and  wastefulness  of  U-pipe  stoves. 

From  the  testimony  on  which  this  review  is  based,  as 
well  as  from  a  number  of  private  communications,  it 
seems  doubtful  if  the  pre-heating  of  the  blast  effects 
any  improvement  in  the  degree  of  concentration  when 
smelting  a  heavy  sulphide  charge.  As  this  matter  of 
concentration  is  a  very  important  one,  and  as  there  is  a 
large  class  of  metallurgists  who  have  as  yet  had  no  ex- 
perience in  this  kind  of  smelting,  and  feel  in  doubt  as  to 
what  types  of  ores  are  most  benefited  by  pre-heating  the 
blast,  I  shall  take  the  liberty  of  going  into  the  subject 
in  some  detail. 

I  suppose  that,  in  the  pyritic  furnace,  any  degree  of 
desulphurization  can  be  obtained,  by  using  ample  blast, 
and  provided  there  is  sufficient  free  silica  to  retard  the 
smelting  operation  and  combine  with  the  ferrous  oxide 
formed  by  the  burning  of  the  sulphides.  Theoretically, 
all  of  the  sulphur  could  be  burned  off,  and  even  the 
copper  scorified  and  carried  into  the  slag,  if  desired. 
Practically,  such  a  complete  oxidation  as  this  would  be 

*  See  page  124. 
9  148 


E.  D.  PETERS. 

very  difficult  to  accomplish,  owing-  to  the  lack  of  heat 
after  the  combustible  portions  of  the  charge  have  been 
consumed. 

If,  for  experimental  purposes,  we  should  endeavor  to 
accomplish  such  an  unprofitable  feat  as  this,  we  would 
find  that  the  addition  of  carbonaceous  fuel,  beyond  a 
certain  moderate  limit,  would  nullify  the  result  desired, 
as  it  would  simply  cause  the  still  remaining  sulphides  to 
melt  down  without  decomposition,  thus  producing  the 
very  matte  that  we  were  trying  to  avoid  producing,  and 
also  robbing  the  free  silica  of  the  ferrous  oxide  which  is 
necessary  for  a  flux.  We  can  use  a  small  amount  of 
carbonaceous  fuel — say  2  to  6  per  cent  coke — and  still 
blow  in  enough  air  to  maintain  the  powerfully  oxidizing 
atmosphere  that  must  be  kept  up  if  we  are  to  effect  the 
thorough  scorification  of  each  and  everv  constituent 
of  the  charge  that  is  capable  of  being  scorified ;  but,  as 
the  slow-sinking  charge  approaches  the  zone  of  fusion, 
it  becomes  more  and  more  helpless  as  a  source  of  heat. 
There  has  been  long-continued  and  powerful  oxidation 
going  on  for  several  feet  above  the  smelting-  zone,  and, 
although  all  the  constituents  of  the  charge  have  been 
heated  to  so  high  a  temperature  that  the  small  propor- 
tion of  sulphides  that  still  remains  undecomposed  is 
almost  ready  to  melt,  while  the  silica  requires  only  a  few 
hundred  degrees  more  heat  to  fit  it  to  combine  with  the 
ferrous  oxide  that  will  result  from  the  burning  of  these 
remaining  sulphides,  we  shall  find  that  there  is  not 
quite  enough  heat  left  to  complete  the  process.  Most 
of  the  oxidizable  constituents  of  the  charge  have  already 
been  oxidized,  and,  as  soon  as  a  substance  has  been 
ozidized,  it  ceases  to  exist  as  a  source  of  heat.  It  is 
inert  and  dead,  and  absorbs,  instead  of  producing,  heat. 

The  furnace  is  in  the  same  condition  that  a  converter 
is  in  when  we  start  to  blow  white  metal  up  to  blister 
copper  without  having  an  excess  of  heat  stored  up  in 
its  walls.  We  have  no  proper  fuel  left  in  the  charge; 

149 


PYRITE    SMELTING. 

the  20  per  cent  of  sulphur  combined  with  the  copper  is 
but  a  feeble  source  of  heat,  and  our  reliable  fuel — the 
iron  content  of  the  matte — has  been  removed  in  a  pre- 
vious operation.  To  prevent  chilling,  extraneous  heat 
must  be  procured  from  some  source  or  another,  and,  in 
practice,  this  is  usually  effected  by  adding:  a  quantity  of 
lower-grade  matte,  the  combustion  of  which  furnishes 
not  only  the  heat  required  to  melt  the  white  metal  thor- 
oughly, but  also  to  warm  up  the  converter  lining  to  a 
point  sufficient  to  carry  the  copper  through  the  finishing 
stages  of  converting,  where  it  cannot  itself  supply  heat 
enough  to  keep  the  charge  thoroughly  melted.  The 
converting  of  copper  matte  to  blister  copper  without  ex- 
traneous heat  would  be  impossible,  and,  as  has  just 
been  shown,  this  extraneous  heat  is  obtained  by  storing 
up  caloric  in  the  converter  walls  during  the  stage  of 
the  process  where  we  are  generating  an  excess  of  heat, 
and  drawing  upon  this  source  during  that  stage  in 
which  insufficient  heat  is  being  produced. 

In  pyrite  smelting  in  the  blast  furnace,  it  is  impos- 
sible to  store  up  excess  heat,  to  be  drawn  upon  when 
needed  later ;  we  lack  sufficient  undecomposed  sulphides 
in  the  charge  to  augment  the  heat  required  at  the 
moment  of  fusion ;  and  we  are  debarred  from  the  use  of 
sufficient  carbonaceous  fuel  to  supply  what  is  wanting. 
The  balance  seems  to  be  struck  just  about  at  the  point 
of  fusion,  and  the  addition  or  the  subtraction  of  a  few 
thousand  units  of  heat  just  at  this  critical  moment  will 
make  the  difference  between  successfully  melting  the 
charge,  or  freezing  up  the  furnace.  It  is  under  such 
conditions  as  these  that  the  pre-heating  of  the  blast, 
even  to  a  very  moderate  degree,  will  turn  the  scale ;  and 
it  is  because  they  are  dealing  with  (approximately)  such 
conditions  that  Koch  and  Bretherton  insist  upon  the 
heated  blast,  not  as  advantageous^  but  as  indispensable, 
while  those  gentlemen  who  are  smelting  heavy  sul- 
phides regard  it  as  a  luxury  rather  than  a  necessity. 

150 


E.  D.  PETERS. 

3.    SAVING  OF  COKE. 

The  question,  "To  what  extent  can  fuel  be  elimi- 
nated ?"  cannot  be  answered  categorically,  if  it  is  to  con- 
vey accurate  information.  It  can  be  said  in  a  general 
way  that,  other  things  being  equal,  the  percentage  of 
coke  to  be  used  in  any  given  case  stands  in  inverse  pro- 
portion to  the  oxidizable  constituents  of  the  charge.  Or, 
in  plain  language,  when  a  charge  contains  its  own  fuel 
in  the  shape  of  iron  sulphides  or  arsenides,  we  need  not 
add  so  much  outside  fuel  to  melt  it.  And  it  is  not  only 
that  we  are  not  obliged  to  use  as  much  extraneous  fuel ; 
we  can  not  use  it,  if  we  expect  to  get  any  reasonable  de- 
gree of  concentration. 

If  an  ore  is  full  of  sulphides,  and  we  desire  to  obtain  a 
fairly  concentrated  matte,  the  only  way  that  it  can  be 
done  is  to  burn  the  sulphur  to  sulphur  dioxide  and  send 
it  out  of  the  stack ;  and  burn  the  ferrous  sulphide  to  fer- 
rous oxide  and  send  it  into  the  slag;  these  objects 
cannot  be  accomplished  unless  two  conditions  are  pres- 
ent: i,  an  oxidizing  atmosphere;  and  2,  an  excess  of 
free  silica. 

To  obtain  this  oxidizing  atmosphere,  we  must  reduce 
the  coke  until,  when  blowing  a  reasonable  blast  into  the 
furnace,  there  will  be  enough  oxygen  not  only  to  burn 
the  coke,  but  also  to  produce  a  highly  oxidizing  atmos- 
phere with  which  to  burn  the  sulphides ;  for,  when  an 
atom  of  oxygen  has  to  choose  between  an  atom  of 
glowing  coke  and  an  atom  of  glowing  sulphide,  it  pre- 
fers to  combine  with  the  coke,  and  the  sulphide  simply 
melts  as  ferrous  sulphide  and  goes  into  the  matte  as 
such,  and  it  is  only  the  excess  of  oxygen  that  acts  upon 
the  sulphides.  Consequently,  when  smelting  a  heavy 
sulphide  ore,  with  the  determination  of  obtaining  a  con- 
siderable degree  of  concentration,  the  question,  "How 
much  can  I  cut  down  the  coke  ?"  is  an  entirely  inappro- 

151 


PYRITE  SMELTING. 

priate  one.  It  actually  seems  to  me  sometimes  that 
it  would  be  more  correct  to  ask :  "How  much  coke  do  I 
dare  to  use  ?"  For  the  experimenter  will  soon  find  that 
it  is  the  degree  of  concentration  required  that  will 
answer  these  questions.  Assuming  that  other  condi- 
tions are  favorable,  and  that  he  has  ample  free  silica 
in  his  ore,  he  must  keep  carefully  lessening  his  coke 
until  the  required  degree  of  concentration  is  attained. 

It  is  nervous  work  when  one  first  tries  it ;  but,  if  the 
charge  is  suitably  made  up  for  genuine  pyritic  work,  it 
will  be  found  that,  although  the  behavior  and  the  in- 
terior appearance  of  the  furnace  will  exhibit  marked 
changes  as  it  shifts  its  fuel  from  coke  to  sulphides,  the 
smelting  will  proceed  satisfactorily,  though  slowly,  and 
the  supply  of  heat  will  be  ample.  I  will  indicate,  how- 
ever, one  danger  to  be  avoided  as  it  has  been  the  cause 
of  trouble  in  several  experiments  that  have  come  to  my 
knowledge,  namely,  as  the  coke  is  lessened,  the  lime- 
stone (if  such  is  being  used)  must  also  be  lessened,  or 
the  silica  increased — which  is  virtually  the  same  thing. 
Reference  to  this  point  will  appear  too  elementary  to 
the  contributors  to  this  discussion,  but  it  will  be  useful 
in  many  instances.  This  necessity  of  lessening  the 
limestone,  or  increasing  the  silica,  arises,  of  course, 
from  the  fact  that,  as  the  proportion  of  coke  is  lessened, 
the  sulphides  are  burned  more  vigorously,  and  the  re- 
sulting ferrous  oxide  requires  silica  to  slag  it.  The 
charge,  therefore,  is  now  more  basic  than  it  was  when 
coke  was  being  burned  as  a  fuel,  and,  unless  the  ferrous 
oxide  is  offered  the  necessary  free  silica  to  combine 
with,  troubles  will  arise,  and  the  degree  of  concentra- 
tion will  drop  again. 

An  oxidizing  atmosphere  is  the  distinguishing  charac- 
teristic of  pyrite  smelting,  and  heat  is  one  of  its  prin- 
cipal products.  Consequently,  an  ore  that  contains 
considerable  quantities  of  suitable  oxidizable  constitu- 
ents, such  as  pyrite,  is  capable  of  yielding  considerable 

152 


E.  D.  PETERS. 

quantities  of  heat,  and  thus  requires  but  little  coke  for 
its  smelting";  and  vice  versa. 

Austin  speaks  very  conservatively  as  to  the  extent  to 
which  carbonaceous  fuel  may  be  reduced,  and  states 
that,  with  an  abundance  of  sulphide  ore,  the  amount  of 
coke  has  been  cut  to  6  per  cent  and  less.  No  doubt  he 
is  referring  solely  to  cases  where  there  is  a  tolerably 
high  ratio  of  concentration  (and,  consequently,  a  sili- 
cious  charge),  for  much  so-called  pyritic  smelting-  has 
been  done  for  years  with  one-third  as  much  fuel  as 
this. 

Beardsley  comes  direct  from  the  great  Mount  Lyell 
smelter,  where  there  is  a  maximum  amount  of  sul- 
phides, and  where  the  ratio  of  concentration  is  moder- 
ate, say  7  to  i,  and  tells  us  that,  when  running-  with  a 
portion  of  the  charge  consisting  of  certain  ores,  2,\  to 
3  per  cent  coke  is  required,  while,  with  the  same  propor- 
tion of  the  charge  consisting  of  certain  other  ores  of  an 
almost  identical  chemical  composition,  the  charge  is 
smelted  with  from  0.3  to  0.4  per  cent  coke.  This  result 
is,  as  far  as  I  am  aware,  the  lowest  point  to  which  the 
proportion  of  coke  to  charge  has  been  reduced,  with 
anything  like  this  ratio  of  concentration,  and  with  cam- 
paigns of  from  60  to  80  days.  The  result  is  also  at- 
tained with  an  unheated  blast. 

Beardsley  adds:  "At  Mount  Lyell,  as  the  charge 
column  was  gradually  raised,  and  the  blast  increased, 
the  stove  heat  was  taken  off,  until,  finally,  stoves  were 
not  used  at  all-."  This  shows  positively  that,  with  a 
high  ore-column,  a  powerful  blast,  and  heavy  pyritous 
ores,  the  furnace  may  make  long  campaigns  on  a  coke 
charge  of  less  than  one-half  of  one  per  cent,  providing 
the  physical  make-up  of  the  ore  is  suitable. 

Let  us  see  what  physical  condition  of  the  ore  is  un- 
suitable, as  this  is  an  important  point,  and  one  that  we 
have  but  little  information  on,  in  connection  with  pyritic 
smelting.  Every  one  will  agree  that  the  presence  of  a 

153 


PYRITE    SMELTING. 

considerable  proportion  of  fines  is  quite  disadvantage- 
ous in  any  kind  of  smelting  in  the  blast  furnace.  It  is 
doubly  harmful  in  pyrite  smelting,  and  is  especially 
emphasized  by  Nutting,  who  suffers  from  having  most 
of  his  sulphide  ores  in  a  finely  divided  condition.  These 
fine,  heavy,  fusible  sulphides  run  down  between  the 
coarser  lumps  of  ore  until  they  reach  the  smelting  zone, 
while  an  infusible  silicious  skeleton  is  left  behind. 
Beardsley,  however,  calls  attention  to  a  still  different 
circumstance,  and  one  which  appears  to  have  a  much 
greater  influence  upon  the  process  than  we  should 
anticipate,  especially  considering  the  enormous  fur- 
naces and  powerful  blast  at  the  Mount  Lyell  plant.  His 
ore  consists  of  a  massive  pyrite,  to  which  must  be  added 
sufficient  silica  and  earthy  bases  to  form  a  suitable  slag. 
He  describes  two  different  kinds  of  silicious  ores  which 
are  employed  as  a  flux.  The  first  kind  consists  of  a 
silicious  aluminous  schist,  containing  from  4  to  8  per 
cent  copper  as  .bornite,  and  about  5  per  cent  iron  as 
pyrite.  The  sulpnide  minerals  in  this  schist  occur  in 
concentrated  and  isolated  patches  throughout  the 
gangue,  and  when/this  class  of  ore  is  used  as  a  silicious 
flux,  the  campaigns  are  short,  and  the  charge  requires 
2\  to  3  per  cent  coke.  The  second  variety  of  silicious 
flux  is  also-  a  schist,  having  approximately  the  same 
chemical  composition  as  the  preceding  ore,  except  that 
it  contains  about  8  per  cent  iron,  and  only  \\  per  cent 
copper.  But  in  this  schist,  the  sulphides  are  dissemi- 
nated in  little  grains  pretty  evenly  throughout  the 
gangue.  When  using  this  second  variety  of  schist,  the 
campaigns  last  from  60  to  80  days,  and  only  0.3  to  0.4 
per  cent  coke  is  required. 

I  think  that  I  am  fairly  interpreting  the  replies  to  this 
question  when  I  say  that,  in  pyrite  smelting,  the  pro- 
portion of  coke  may  be  reduced  to  almost  nothing  in 
the  case  of  heavy  sulphide  ore  of  favorable  physical 
make-up,  and  where  the  ratio  of  concentration  is  not 

154 


E.  D.  PETERS. 

very  high,  and  that  the  amount  of  coke  increases  as 
the  proportion  of  sulphide  diminishes,  and  also  in- 
creases (within  narrow  limits)  as  the  degree  of  concen- 
tration increases ;  but  that,  even  with  high  concentra- 
tion, and  with  quite  a  low  proportion  of  sulphide,  a 
marked  saving  in  coke  is  effected  by  running  the  fur- 
nace pyritically. 


4.  COPPER  A  COLLECTOR  OF  THE  PRECIOUS  METALS. 

The  question  of  the  amount  of  copper  required  for 
the  collection  of  the  precious  metals  is  of  much  interest 
to  those  who  are  engaged  in  the  smelting  of  copper  ores 
by  any  process,  and  is  doubly  important  where  pyrite 
smelting  is  practised.  Copper  ores  frequently  contain 
values  in  gold  and  silver,  and  the  ordinary  blast  furnace 
smelter  often  finds  it  advantageous  to  buy  outside  gold 
and  silver  ores  containing  little  or  no  copper,  provided 
they  are  not  too  silicious  for  his  charge ;  but  this  italicized 
limitation  cuts  him  off  from  a  great  part  of  all  the  pre- 
cious metal  ores  on  this  continent. 

Nor  is  this  all.  He  is  also  cut  off  from  another  great 
class  of  ores,  which  are  not  much  wanted  by  either  lead 
or  copper  smelters,  and  on  which  there  is,  accordingly, 
a  quite  profitable  treatment  charge.  I  refer  to  dry  ores 
of  only  moderate  richness  in  gold  and  silver,  and  con- 
taining, perhaps,  I  or  2  per  cent  copper,  3  or  4  per  cent 
lead,  a  little  arsenic  and  antimony,  several  per  cent  of 
zinc-blende,  and  enough  pyrite  to  bring  the  total  sul- 
phur contents  up  to  10  or  12  per  cent.  Such  ores  con- 
tain too  much  sulphur  to  smelt  raw  either  in  the  copper 
or  the  lead  furnace,  and  yet  scarcely  enough  to  pay  to 
roast  them,  and  being  usually  silicious  as  well,  are  not 
regarded  with  favor  by  the  average  metallurgist. 

Yet  these  very  ores  that  I  have  been  describing  are 
among  the  most  advantageous  that  the  pyrite  smelter 
can  desire.  With  the  aid  of  the  hot  blast,  he  may  ex- 

155 


PYRITE    SMELTING. 

pect  to  completely  volatilize  the  lead,  arsenic,  and  anti- 
mony, and  to  either  slag  or  volatilize  the  zinc.  He  can 
obtain  almost  any  degree  of  concentration  that  he  de- 
sires, and  the  heat  produced  by  the  oxidation  of  even 
this  very  moderate  proportion  of  sulphides  will  effect 
quite  a  saving  in  coke.  There  is  so  little  copper  in  these 
ores  that,  although  promptly  giving  up  their  gold  and 
silver  values  to  the  matte,  they  add  very  little  to  its 
weight.  Hence,  the  refining  charges  per  ton  of  original 
ore  will  be  small,  and  the  conditions  for  close  saving  of 
values  are  so  favorable,  that  the  1.3  per  cent  copper  de- 
ducted in  accounting  for  what  little  of  that  metal  may  be 
present,  will  generally  pay  for  the  limestone  that  must 
be  added  to  flux  the  excess  of  silica  that  these  ores  usu- 
ally carry. 

The  smelting  of  these  dry  silicious,  precious  metal 
ores,  which  will,  of  course,  be  mixed  with  more  massive 
pyritous  material,  seems  to  me  to  be  the  especial  prov- 
ince of  pyrite  smelting.  A  typical  instance  of  this  kind 
may  be  found  in  Bretherton's  excellent  work  at  the  Val 
Verde  smelter,  in  Arizona. 

Eight  of  the  correspondents  have  replied  to  this  ques- 
tion so  simply  and  specifically  that  it  is  possible  to  make 
a  little  table  of  their  figures. 

COPPER  REQUIRED   TO  COLLECT   GOLD  AND  SILVER. 

Austin 0.5 

Beardsley 1.5    Has  never  had  experience  with  less. 

Carpenter 1.0  and  less. 

•      Fulton 0.5 

Koch 0.5 

Lloyd 0.5  and  less. 

Mathewson.  ...  0.0 

Nutting 0.5 

There  is  a  remarkable  uniformity  in  these  replies. 
An  average,  or  composite,  answer  to  a  question  of  this 
kind  is,  of  course,  almost  worthless  where  the  replies 
vary  much ;  but,  in  the  present  case,  they  are  so  nearly 
identical  that  I  will  give  the  average  result  of  the  re- 

156 


E.  D.  PETERS. 

plies,  omitting  the  answers  of  Messrs.  Beardsley  and 
Mathewson:  the  former,  because  he  says  that  he  has 
not  had  occasion  to  try  the  minimum  limit ,  the  latter, 
because  he  contends  that  no  copper  at  all  is  necessary, 
as,  indeed,  do  one  or  two  of  the  other  gentlemen,  un- 
der certain  conditions.  The  average  of  the  remaining 
replies  is  0.643  Per  cent — or>  sav  two-thirds  of  one  per 
cent — as  the  amount  of  copper  in  the  furnace  charge 
that  is  sufficient  to  make  a  satisfactory  collection  of  the 
gold  and  silver  under  favorable  conditions. 

Let  us  see  what  the  various  correspondents  regard 
as  "favorable  conditions."  Austin  says :  "A  charge  con- 
taining sulphide  ores,  but  quite  free  from  copper,  will 
not  give  a  clean  slag;  but,  with  as  little  as  0.5  per  cent 
copper,  this  object  can  be  attained."  He  mentions  vari- 
ous conditions  as  favoring  the  production  of  a  clean 
slag;  such  as,  absence  of  zinc,  fusibility,  reasonable  dif- 
ference in  specific  gravity  of  matte  and  slag. 

Beardsley  has  never  had  occasion  to  go  below  1 .5 
per  cent  copper  in  the  charge,  and,  down  to  that  point, 
has  always  had  clean  slags.  This  has  been  mostly  with 
a  concentration  of  about  7  to  i,  and  with  a  ferruginous 
slag,  rather  low  in  silica  for  pyrite  smelting,  and  con- 
taining only  about  13  per  cent  of  earthy  bases. 

Bretherton,  who  is  smelting  a  silicious  charge  rather 
high  in  earthy  bases,  tolerably  rich  in  precious  metals, 
and  making  a  concentration  of  anywhere  from  12  to  20 
into  i,  requires  I  per  cent  copper,  and  prefers  3  per 
cent. 

Carpenter  bases  his  reply  upon  the  percentage  of  cop- 
per the  resulting  matte  should  contain,  rather  than 
upon  the  proportion  of  copper  that  should  be  in  the 
charge  before  smelting.  He  also  lays  stress  upon  the 
quantity  of  matte  produced,  and  intimates  that  a  large 
fall  of  matte  containing  only  2  or  3  per  cent  copper 
(original  charge)  might  answer  the  purpose  of  collec- 
tors as  well  as  a  10  per  cent  matte,  if  the  latter  is  pro- 

157 


PYRITE    SMELTING. 

duced  only  in  small  quantity.  He  also  adds :  "If  the 
ores  carry  both  gold  and  silver,  and  a  fair  quantity  of 
matte  is  made,  copper  may  be  entirely  avoided." 

In  connection  with  this  reply,  those  interested  should 
read  Dr.  Carpenter's  interesting  paper  on  Tyritic 
Smelting  in  the  Black  Hills. '  He  had  noticed  that  an 
increase  in  the  grade  of  the  matte  beyond  10  per  cent 
copper  did  not  increase  its  virtue  as  a  collector  of  the 
precious  metals,  and  that  even  a  30  or  40  per  cent  matte 
was  no  better  than  the  lower  grade  indicated.  (The  ad- 
vantage of  the  richer  matte  might  become  obvious  if  the 
slag  were  basic  or  highly  ferruginous,  owing  to  the 
higher  specific  gravity  of  matte  rich  in  copper.) 

Fulton,  in  smelting  the  silicious  gold  ores  of  the  Black 
Hills,  South  Dakota,  at  the  Rapid  City  smelter,  makes 
a  slag,  which  I  take  the  liberty  of  averaging  as  follows : 
Silica,  48  per  cent ;  ferrous  oxide,  18 ;  lime,  28,  and  al- 
umina, 5  per  cent.  This  is  a  pretty  silicious  slag,  the  oxy- 
gen-ratio of  acid  to  base  being  2.33  to  I,  provided 
alumina  is  reckoned  on  the  acid  side,  as  is  the  Mansfeld 
custom ;  indeed,  it  seems  to  me  an  even  tougher  prop- 
osition than  Carpenter's  average  slags  at  the  Deadwood 
&  Delaware  smelter,  as  the  latter  had  about  one-third 
of  this  lime  replaced  by  magnesia,  which  gives  a  better 
slag  than  straight  lime.  So,  as  iron  oxide  is  low,  and 
lime  is  the  only  other  base,  it  must  have  a  high  forma- 
tion temperature;  but,  once  thoroughly  melted,  should 
admit  of  an  excellent  separation  of  the  matte.  The 
smelting  charge  proper  contains  only  traces  of  copper, 
and  it  was  found  that  the  slags  frequently  ran  $1.50  to 
$2  per  ton  in  gold.  As  in  the  Deadwood  smelter,  it 
was  noticed  that  when  the  smelting  conditions  were 
such  that  a  certain  amount  of  metallic  iron  was  formed 
during  the  fusion,  the  slags  would  be  clean,  but  the  for- 
mation of  this  metallic  iron  could  not  be  satisfactorily 

^Transaction  American  Institute  Mining  Engineers,  Vol.  XXX.  page 

158 


E.  D.  PETERS. 

controlled.  Recourse  was  had  to  copper  as  a  col- 
lector, and  just  sufficient  (unprofitable)  Montana  cop- 
per ore  is  now  added  to  bring  the  slag  values  down  to 
25  cents,  or  less,  per  ton.  This  is  accomplished  by  add- 
ing 10  Ib.  copper  for  each  ounce  of  gold  present,  which, 
I  think,  is  about  0.5  per  cent  copper  on  the  charge.  Mr. 
Fulton  finds  that  even  this  addition  of  copper  does  not 
collect  the  small  amount  of  silver  present  so  thorough- 
ly as  it  does  the  gold.  (See  'Sulphide-Smelting  at  the 
National  Smelter  of  the  Horseshoe  Mining  Co.,  Rapid 
City,  S.  D.'  By  Messrs.  Fulton  and  Knutzen.)1 

Koch  at  the  Magistral  mine,  in  Durango,  Mexico, 
is  smelting  an  ore  that  is  tolerably  free  from  metals  or 
metalloids  that  might  modify  or  obscure  the  behavior 
of  pure  iron-copper  matte  as  a  collector  of  the  precious 
metals.  His  charge  averages  0.5  per  cent  copper,  and 
about  0.5  oz.  gold  and  0.25  oz.  silver  per  ton.  He  makes 
a  concentration  of  15  into  I,  with  the  production  of  a  7 
to  8  per  cent  copper  matte,  and  his  slags  are  clean. 

Lang  holds  that  the  quality,  rather  than  the  quantity, 
of  the  matte  formed  is  the  most  important  factor,  and 
that  a  matte  comparatively  high  in  copper  is  essential, 
if  there  is  a  strongly  ferruginous  slag.  He  thinks  that 
if  an  iron  matte  is  to  be  a  satisfactory  collector,  the  ac- 
companying slag  must  contain  a  fair  proportion  of 
earths.  This,  I  think,  in  no  way  disagrees  with  the  opin- 
ions of  the  other  correspondents. 

Lloyd  states  that,  with  a  matte  under  100  oz.  silver 
and  30  oz.  gold  per  ton,  a  charge  having  a  copper  tenor 
of  0.5  per  cent,  or  even  less,  will  make  a  close  saving. 
He  cites  cases  from  his  own  experience  where  he  has 
done  clean  work  with  even  less  copper.  (The  instances 
referred  to  by  Mr.  Lloyd  would  be  even  more  valuable 
if  the  average  composition  of  the  slag  were  also  indi- 
cated. A  matte  that  may  answer  as  an  excellent  collec- 
tor where  there  is  a  silicious  or  earthy  slag  may  be 

^Transactions  American  Institute  Mining  Engineers,  1904. 

159 


PYRITE    SMELTING. 

quite  unsatisfactory  where  the  slag  is  basic  or  highly 
ferruginous.) 

Mathewson  gives  a  concise  and  emphatic  answer  to 
this  question.  He  says :  "Copper  is  not  necessary  for 
the  collection  of  the  precious  metals.  They  will  collect 
readily  in  an  iron  matte." 

Nutting,  with  whom  zinc-blende  is  ever  present,  says 
that,  when  this  mineral  is  absent,  a  fair  collection  can 
be  made  without  any  copper,  but  that  the  beneficial  ef- 
fects of  even  0.5  per  cent  will  be  recognized.  With  a 
considerable  amount  of  blende  in  the  charge,  he  would 
desire  1.5  to  2  per  cent  copper,  to  induce  a  better  sep- 
aration of  matte  and  slag. 

Ingalls  found  that  in  smelting  an  ore  containing  50 
oz.  silver  and  i  oz.  gold  per  ton,  and  I  per  cent  copper, 
he  made  satisfactory  recoveries.  He  believes,  however, 
that  if  much  blende  were  present,  it  would  take  more 
copper,  so  that  the  separation  of  matte  and  slag  might 
be  easier. 

There  seems  to  be  a  pretty  complete  unanimity  of 
opinion  that  a  very  small  percentage  of  copper  in  the 
charge  will  suffice  as  a  collector  for  gold  and  silver,  pro- 
vided that  the  slag  is  favorable  for  the  mechanical  sep- 
aration of  the  matte. 

One  per  cent  of  the  weight  of  the  charge  in  copper, 
and  less  rather  than  more,  would  appear  to  satisfy  the 
requirements  of  the  gentlemen  represented  in  this  dis- 
cussion, provided  the  slag  is  not  too  heavy  in  iron,  or 
does  not  contain  an  excessive  amount  of  zinc  oxide. 

Several  of  the  contributors  to  the  recent  discussion 
state  that  an  iron  matte,  free  of  copper,  forms  a  satis- 
factory collector  of  the  precious  metals  under  suitable 
conditions.  Others,  evidently,  have  not  found  this  to 
be  the  case ;  but  positive  evidence  is  better  than  nega- 
tive, and  in  the  light  of  such  unimpeachable  statements 
as  we  now  have  on  the  subject,  we  may,  I  think,  accept 

160 


E.  D.  PETERS. 

as  a  fact  that,  under  favorable  conditions,  a  matte  free 
from  copper  will  collect  the  precious  metals  satisfac- 
torily. 

The  question  at  once  arises :  What  are  these  favorable 
conditions?  As  has  been  already  stated,  a  rather  sili- 
cious,  liquid  slag  of  low  specific  gravity  is  highly  advan- 
tageous, for,  without  this,  the  light  iron  matte  will  find 
it  difficult  to  settle  properly. 

There  are,  however,  other  factors  that  profoundly  in- 
fluence the  collection  of  the  precious  metals  in  an  iron 
matte;  and,  in  order  that  this  most  interesting  point 
may  not  be  left  incomplete,  I  shall  take  the  liberty  of 
discussing  briefly  some  of  the  other  conditions  that  bear 
upon  it. 

In  the  first  place,  this  question,  though  most  impor- 
tant to  the  pyrite  smelter,  does  not  belong  any  more  to 
him  than  it  does  to  the  ordinary  smelter  of  roasted  ore. 
For  many  generations  past,  therefore,  whenever  the 
copper  metallurgist  has  been  smelting  sulphide  ores 
containing  gold  or  silver,  whether  in  blast  furnaces  or 
reverberatories,  and  whether  raw  or  roasted,  he  has 
been  accumulating  facts  that  bear  directly  upon  this 
question.  It  would  seem,  therefore,  that  by  this  time 
we  ought  to  possess  enough  information  on  the  subject 
to  enable  us  to  say  positively  that,  when  making  a  slag 
of  such  and  such  a  composition,  and  with  a  charge  of 
such  richness  in  gold  and  silver,  our  matte  must  contain 
so  and  so  much  copper  in  order  to  be  an  efficient  collec- 
tor of  the  precious  metals  present.  As  a  matter  of  fact, 
we  can  do  nothing  of  the  kind ;  and,  in  smelting  two  dif- 
ferent ores,  having  the  same  values  in  precious  metals 
and  yielding  a  slag  of  identical  composition,  we  may 
easily  find  that,  in  the  one  case,  a  matte  entirely  free 
from  copper  will  prove  an  efficient  collector  of  values, 
while  in  the  other  the  matte  must  contain  several  per 
cent  of  copper  in  order  to  clean  the  slags  effectually. 

With  the  object  of  inviting  discussion,  I  will  suggest 

161 


•       PYRITE  SMELTING. 

the  following  factors  as  having  a  bearing  upon  the  col- 
lection of  the  gold  and  silver  in  an  iron  matte. 

1.  The  physical  make-up  of  the  ore. 

2.  The  influence  of  certain  substances  that  often  ac- 
company the  precious  metals  in  very  minute  quantities. 

3.  The  formation  during  the  operation  of  smelting, 
of  certain  substances  that  may  act  as  collectors. 

1.  The  physical  makeup  of  the  ore  is  probably  the  least 
important  of    the  three  factors  just    enumerated,  but 
must,  I  think,  be  recognized  in  certain  ores.     It  is  im- 
possible to  discuss  the  point  properly  except  at  length, 
but  I  have  several  times  convinced  myself  that,  in  cer- 
tain cases  where  free  eold  or  tellurides  exist  in  minute 
specks  throughout  massive  quartz,  and  the  amount  of 
matte  made  is  small  and  is  produced  from  coarse  iron 
sulphides   that   are   not   disseminated    throughout    the 
same  ore,  the  slag  may  run  high,  owing  to  want  of  jux- 
taposition between    the  collector  and    the  particles  of 
gold. 

2.  The  influence  of  certain    substances  that   often   ac- 
company   the  precious  metals  in  very  minute  quantities. 
The  attention  of  many  matte  smelters  was  first  directed 
to  this  point  by  Richard  Pearce's  experiments  and  de- 
ductions in  his  paper  entitled  The  Association  of  Gold 
with  Other  Metals  in  the  West.'1    I  know  that  this  pa- 

•  per  cleared  up  for  me  many  obscure  and  apparently 
conflicting  results  encountered  in  the  matte  smelting  of 
certain  gold  and  silver  ores,  at  times  when  my  precari- 
ous supply  of  copper  ores  ran  short.  Mr.  Pearce  shows, 
by  actual  experiment,  that:  "Pure  gold  melted  with 
pure  iron  pyrite  is  not  attacked  in  any  way  by  the  fused 
sulphide  of  iron.  A  matte  is  obtained  in  which  the  gold 
exists  in  a  pure  state,  but  disseminated  through  the 
mass  in  very  fine  globules." 

transactions    American     Institute    Mining   Engineers,     Vol.     XVIII, 
page  447. 

162 


E.  D.  PETERS. 

Mr.  E.  G.  Spilsbury1  described  the  smelting  of  a  mix- 
ture of  raw  and  roasted  pure  iron-pyrite  concentrates, 
carrying  about  two  ounces  in  gold  per  ton.  The  prop- 
erly fluxed  ore  was  smelted  by  Professor  F.  W.  Clark, 
of  the  Massachusetts  Institute  of  Technology,  in  a  small 
reverberatory  furnace.  The  well-melted  slag  contained 
from  i  to  1.6  oz.  gold  per  ton,  and  the  resulting  iron 
matte  assayed  4  to  8  oz.  per  ton,  the  gold  values  being 
very  irregularly  distributed  in  the  matte,  though  the 
slag-  assays  were  comparatively  uniform. 

These  experiments,  in  connection  with  results  ob- 
tained in  my  own  practice,  lead  me  to  believe  that  pure 
iron  sulphide  is  a  very  poor  collector  of  pure  gold  (or 
of  gold  containing  very  little  silver),  and  this  belief  is 
held,  I  think,  by  most  metallurgists  whose  attention 
has  been  called  to  the  matter.  It  appears  that,  in  such 
cases,  the  gold  is  simply  held  in  mechanical  suspension 
in  the  matte,  and  not  in  solution,  as  Pearce  expresses  it. 
The  same  observer  found  further,  that  the  presence  of 
minute  proportions  of  bismuth  (which  occurs  much 
more  frequently  in  connection  with  gold  ores  than  any 
one  realizes,  except,  perhaps,  the  electrolytic  refiner), 
and  perhaps,  also,  tellurium,  caused  a  complete  solution 
of  the  gold  in  the  iron  matte ;  and  it  is  quite  probable 
that  arsenide  and  antimonide  compounds  may  exert  a 
similar  influence. 

It  seems  to  me  probable,  therefore,  that,  in  cases 
where  a  good  collection  of  the  precious  metals  has  been 
made  by  an  iron  matte  free  from  copper,  there  have 
been  present  small  quantities  of  bismuth,  tellurium,  ar- 
senic, antimony  or  other  substances  that  have  aided 
this  collection,  and  that  we  need  a  good  deal  of  accurate 
and  delicate  chemical  investigation  on  this  subject  be- 
fore we  shall  be  able  to  predict,  in  any  given  case, 

^Transactions  American  Institute  Mining  Engineers,  Vol.  XV,  page  767. 
163 


PYRITE    SMELTING. 

whether  we  are  going  to  be  able  to  make  clean  slags 
without  any  copper  in  the  matte.1 

3.  The  formation  during  the  smelting  process  of  cer- 
tain substances  that  act  as  collectors.  That  metallic 
iron,  under  certain  conditions,  will  act  as  a  collector  of 
gold,  though  not  of  silver,  has  long-  been  known  to  met- 
allurgists. More  than  50  years  ago  a  blast  furnace  was 
erected  for  the  purpose  of  smelting  into  metallic  iron 
the  rich  gold-bearing  black  sands  of  the  Siberian  placer 
mines.  It  is  said  to  have  yielded  clean  slags,  and  a  pig- 
iron  rich  in  gold.  It  was  eventually  given  up,  owing  to 
the  expense  of  separating  the  gold  from  the  pig-iron, 
and  the  difficulty  of  controlling  the  reduction  of  the 
iron  oxides  in  the  furnace. 

The  originator  of  the  process  hoped  to  be  able  to  slag 
a  large  proportion  of  the  oxidized  iron  as  ferrous  oxide, 
and  to  reduce  just  sufficient  of  it  to  obtain  a  moderate 
amount  of  metallic  iron  rich  in  gold.  This  he  was  un- 
able to  do  with  any  certainty,  as,  if  he  reduced  enough 
of  the  oxides  to  metallic  iron  to  obtain  clean  slags,  he 
found  that,  before  he  could  stop  it,  nearly  all  of  the  ox- 
idized iron  in  the  charge  would  be  reduced  to  the  me- 
tallic state,  thus  producing  a  large  amount  of  low-grade 
metal  and  robbing  his  slag  of  its  needed  flux. 

This  experience  is  useful  to  us  as  showing  that  metal- 
lic iron  has,  at  least,  some  power  in  collecting  gold; 
but,  apart  from  this,  it  is  of  little  interest  to  the  matte 
smelter,  as  the  conditions  are  completely  changed  by 
the  presence  of  sulphides  in  the  charge. 

For  the  true  pyrite  smelter,  it  has  an  even  more  re- 
mote bearing;  for  not  only  may  the  presence  of  sul- 
phides in  the  furnace  obscure  the  reactions,  but  the  me- 
tallic iron  that  he,  under  certain  conditions,  produces 
is  a  totally  different  substance  from  the  metallic  iron 

iSince  the  completion  of  this  article,  I  have  received  a  copy  of  a  pa- 
per by  Mr.  Myrick  N.  Bolles,  B.  S.,  to  appear  in  the  Transactions  A.  I. 
M.  B.  for  1904,  entitled,  'The  Concentration  of  Gold  and  .Silver  in  Iron 
Bottoms' ;  this  contains  much  valuable  original  work  on  the  matter  dis- 
cussed under  this  head.— E.  D.  P. 

164 


E.  D.  PETERS. 

produced  in  smelting  the  Siberian  black  sand  with  coke. 
The  cause  of  this  difference  is  obvious.  In  the  coke 
furnace,  as  run  on  these  Siberian  black  sands,  the  prod- 
uct was  simply  cast-iron  ;  the  reduction  was  effected 
by  the  carbon,  and  the  resulting  iron  contained  carbon, 
as  does  ordinary  pig-iron.  In  the  pyritic  furnace,  the 
atmosphere  averages  distinctly  oxidizing;  else  the  sul- 
phur would  not  be  burned,  nor  the  iron  be  changed  into 
ferrous  oxide,  nor  would  it  be  'pyrite'  smelting,  as  I 
am  employing  this  term. 

Consequently,  the  metallic  iron,  which  is  occasionally 
produced  in  considerable  quantities  in  the  pyritic  fur- 
nace, would  appear  to  be  produced  under  distinctly  ox- 
idizing conditions  and  not  to  be  connected  with  the 
presence  of  carbon.  I  know  positively  that  metallic 
iron  can  be  made  by  blowing  a  powerful  blast  into  mol- 
ten sulphide  ores,  when  making  a  very  silicious  slag,  be- 
cause I  once  inadvertently  filled  up  my  hearth  with  an 
iron  sow,  when  trying  to  smelt  raw  sulphide  fines  with- 
out carbonaceous  fuel.  The  fines  ran  down  through  my 
coarser  silicious  ore,  the  result  being  that  the  charge 
soon  froze  solid,  but  not  until  a  sow  of  metallic  iron, 
weighing  several  hundred  pounds,  had  been  formed. 

Dr.  Carpenter  gives  much  valuable  information  on 
this  matter  in  his  paper  on  Tyritic  Smelting  in  the 
Black  Hills.'1  Messrs.  Fulton  and  Knutzen  supple- 
ment this  by  a  more  recent  paper.2 

I  quote  from  the  latter:  "The  matte  formed  rarely 
contains  more  than  30  per  cent  sulphur,  while  the  iron 
monosulphide  contains  36.36  per  cent,  so  that  the  matte 
is  evidently  a  subsulphide.  It  also  contains  metallic 
iron,  which  can  be  readily  abstracted  by  the  magnet. 
We  agree  with  Dr.  Carpenter  that  it  is  this  metallic  iron 
in  the  matte  which  collects  the  gold,  but,  unfortunately, 
it  is  rarely  present  in  the  matte  in  sufficient  quantity  to 

i  Transactions  American  Institute  Mining  Engineers,  Vol.  XXX. 


'Sulphide  Smelting  at  the  National  Smelter  of  the  Horseshoe 
Mining  Company,'  1004. 

165 


PYRITE    SMELTING.  *       . 

give  clean  slags.  Paradoxical  as  it  may  seem,  the  quan- 
tity of  metallic  iron  formed  in  the  furnace  is  due  to  a 
large  extent  to  the  amount  of  oxidation  which  takes 
place  in  the  furnace.  ...  In  our  opinion,  the  pro- 
duction of  sows  is  practically  inseparable  from  sulphide- 
smelting  when  high  concentration  is  done.  The  sows 
are  due  to  the  strong  oxidizing  effect  of  the  furnace,  as 
shown  from  the  following  data :  A  desulphurization  of 
80  per  cent ;  the  production  of  copper  sulphate,  found  in 
layers  in -the  accretions  of  the  downtake;  no  evidence  of 
carbon  monoxide  in  the  furnace  gases;  the  volatilization 
of  all  the  lead  fed  into  the  furnace ;  and  the  facts  that, 
while  no  iron  goes  into  the  furnace  as  oxide,  the  slag 
contains  from  18  to  20  per  cent  of  iron  oxide  in  the  form 
of  silicate.  These  data  make  it  difficult  to  imagine  that 
the  reducing  conditions  in  the  furnace  could  exist  suf- 
ficiently strong  to  produce  metallic  iron. 

We  believe  that  the  sows  are  produced  by  oxidation 
in  a  similar  way  that  metallic  copper  is  produced  during 
bessemerizing ;  taking  as  the  first  stage  the  melting  of 
the  pyrite,  FeS2,  and  the  loss  of  the  one  atom  of  sul- 
phur, thus  forming  the  monosulphide,  FeS ;  the  second 
stage,  the  gradual  oxidation  of  the  sulphur  in  the  mono- 
sulphide,  producing  a  subsulphide ;  the  third  stage,  the 
production  of  some  ferrous  oxide,  part  entering  the  slag 
and  part  reacting  with  the  subsulphide  present,  produc- 
ing sulphur  dioxide  gas  and  metallic  iron,  according  to 
the  following  chemical  equation : 

FeS+2FeO=3Fe+SO2. 

Experience  has  shown  that  a  larger  quantity  and 
higher  pressure  of  blast  result  in  an  increased  produc- 
tion of  metallic-iron  sow,  and,  from  its  analysis,  it  is 
seen  that  it  contains  practically  no  carbon." 

It  seems  possible,  therefore,  that  the  production  of  a 
certain  proportion  of  metallic  iron  in  pyritic  smelting 
may  carry  into  a  pure  iron  matte  gold  value  that  other- 
wise would  not  be  saved. 


166 


E.  D.  PETERS. 

5.   THE  PART  PLAYED  BY  LIME. 

None  of  the  replies  to  the  question  covering  the  per- 
centage of  lime  necessary  to  clean  the  slags,  indicates 
that  any  particular  specific  virtue  is  attached  to  lime 
per  sc,  as  a  cleanser  of  the  slag  from  valuable  metals. 
I  think  I  am  fairly  interpreting  the  unanimous  spirit  of 
the  contributors  by  stating  that  what  they  demand  is  a 
slag  from  which  the  matte  will  separate  satisfactorily; 
that  such  a  slag  must  be  tolerably  silicious,  yet  fusible ; 
and,  moreover,  that  it  is  advantageous  to  have  it  con- 
tain a  fair  proportion  of  earthy  bases,  so  that  it  may 
not  have  too  high  a  specific  gravity.  In  the  great  ma- 
jority of  cases  there  is  no  substance  that  will  fill  the  bill 
so  completely,  and  produce  the  results  just  enumer- 
ated so  cheaply  and  satisfactorily,  as  lime. 

As  a  flux  for  excess  silica,  up  to  a  certain  limit,  i  Ib. 
of  lime  will  go  as  far  as  2.58  Ib.  of  ferrous  oxide.  This 
comes  from  the  fact  that  not  only  is  the  atomic  weight 
of  lime  considerably  smaller  (and,  consequently,  its  oxy- 
gen contents  larger)  than  that  of  ferrous  oxide,  but  that, 
in  the  oxidizing  atmosphere  of  the  pyrite  furnace  (as 
clearly  pointed  out  by  Carpenter  and  Lang),  the  silica 
prefers  to  make  only  a  bisilicate  with  lime,  while  it 
forms  a  singulo-silicate  with  ferrous  oxide ;  and  as  the 
slag  that  we  prefer  to  make  in  pyrite  smelting  will  have 
an  oxygen  ratio  of  acid  to  base  of  somewhere  about  ij 
to  i,  and  is  thus  a  mixture  of  the  bisilicate  of  lime  with 
the  singulo-silicate  of  iron,  it  follows  that,  until  we  have 
reached  our  maximum  desirable  limit  of  lime  in  the 
slag,  each  pound  of  lime  (forming  a  bisilicate)  will  go 
as  far  as  2.58  Ib.  of  ferrous  oxide  (forming  a  singulo- 
silicate). 

The  actual  percentage  of  lime  necessary  to  effect  a 
good  mechanical  separation  of  the  matte  varies  so 
greatly  under  differing  conditions  that  it  is  impossible 
to  lay  down  any  fixed  rules  in  regard  to  it.  A  glance  at 

167 


PYRITE  SMELTING. 

the  large  table  of  questions  and  answers  will  show  that 
most  of  the  replies  are  based  upon  the  local  conditions 
under  which  the  contributor  is  operating-,  and  are  most 
valuable  when  considered  in  connection  with  these  con- 
ditions. 

A  few  of  the  correspondents  have  given  replies  based 
on  more  general  conditions.  Austin  says:  "Slags  con- 
taining as  little  as  5  per  cent  of  lime  have  proved  clean." 

Carpenter  avoids  lime  as  far  as  possible  in  genuine 
pyrite  smelting,  not  that  he  does  not  value  the  type  of 
slag  that  it  makes,  but  because  it  increases  the  quantity 
of  slag,  and  takes  the  place  of  ferrous  oxide  in  combin- 
ing with  silica.  He  says:  "I  think,  all  things  consid- 
ered, and,  especially,  if  the  ores  carry  alumina,  lime  had 
better  be  avoided,  particularly  in  the  first  smelting." 

Lang  values  greatly  the  qualities  of  a  slag  containing 
a  suitable  proportion  of  lime,  but  suggests  that  there 
are  often  occasions  where  it  is  commercially  more  ad- 
vantageous to  get  along  without  it,  and  says  that  rea- 
sonably clean  slags  can  be  made  where  ferrous  oxide  is 
almost  the  sole  base. 

Lloyd  expresses  very  much  the  same  views  as  the 
preceding  writer,  and  emphasizes  the  important  point 
that,  as  a  slag  consisting  mainly  of  ferrous  silicate  is 
heavy,  and  difficult  for  the  matte  to  separate  from,  it 
becomes  all  the  more  necessary,  in  such  cases,  to  pro- 
vide peculiarly  favorable  conditions  for  the  separation 
of  slag  and  matte.  Such,  for  instance,  are  large  fore- 
hearths,  maintained  at  a  high  temperature. 

I  think,  therefore,  that  the  pyrite  smelter  may  assume 
that  lime  has  no  specific  virtue  in  cleansing  the  slags,  but 
that — apart  from  its  great  importance  as  a  basic  flux 
where  too  much  silica  is  present — its  main  value  is  to 
make  the  slag  lighter  in  weight,  so  that  the  matte  glob- 
ules can  separate  more  quickly  and  more  perfectly 
from  it. 

168 


E.  D.  PETERS. 


6.    BEHAVIOR  OF  ZINC. 

The  answers  to  the  question,  "What  percentage  of 
zinc  in  the  charge  can  be  treated  profitably  ?"  are,  on  the 
whole,  the  least  perfect  and  the  least  unanimous  of  any 
of  the  sets  of  replies.  Of  the  ten  contributors  who  ap- 
pear in  the  large  table,  six  do  not  answer  the  question 
at  all,  most  of  them  not  having  had  occasion  to  practise 
pyrite  smelting  on  ores  high  in  zinc.  Our  evidence, 
therefore,  is  limited  to  the  replies  of  Messrs.  Austin, 
Bretherton,  Lloyd  and  Nutting,  together  with  some  in- 
teresting remarks  on  the  same  subject  contained  in  the 
letters  of  Messrs.  Godshall  and  Ingalls. 

Even  with  this  small  amount  of  testimony,  there  is 
some  conflict  of  opinion  as  to  the  behavior  of  zinc  in 
the  furnace.  This  disagreement,  however,  is  apparent 
rather  than  real,  and  arises  simply  from  the  fact  that 
pyrite  smelting  covers  such  a  multiplicity  of  differing 
conditions,  that  almost  any  question  may  elicit  answers 
totally  at  variance  with  each  other,  and  yet,  that  are  not 
in  the  least  conflicting.  In  ordinary  blast  furnace  smelt- 
ing with  coke,  it  may,  I  suppose,  be  accepted  as  a  fact 
that  when  much  zinc-blende  is  present  in  the  charge, 
a  portion  of  it  is  likely  to  enter  the  slag  mechanically 
and  be  carried  away  still  as  a  sulphide;  this  tends  to 
make  the  slag  thick  and  heavy,  and  to  produce  losses 
of  values.  In  the  powerfully  oxidizing  atmosphere  of 
the  pyrite  furnace,  however,  it  does  not  seem  to  me 
possible  that  the  zinc  sulphide  can  behave  in  this  man- 
ner, except  in  those  instances  where  there  is  merely  a 
quick  melting-down  of  the  charge  rather  than  a  genuine 
pyrite  smelting.  Blende  commences  to  burn  at  a  dull 
red  heat,  and  its  oxidation,  in  the  presence  of  an  ample 
air  supply,  is  so  free  and  vigorous,  that  it  is  scarcely 
conceivable  that  any  undecomposed  zinc  sulphide  should 
be  left  to  be  carried  into  the  slag.  Consequently,  I  think 
that,  in  that  variety  of  pyrite  smelting  where  a  high  ra- 

169 


PYRITE  SMELTING. 

tio  of  concentration  is  obtained  by  pushing  the  process 
of  oxidation  to  nearly  its  extreme  limit,  we  can  elim- 
inate this  point  entirely,  and,  for  the  moment,  confine 
our  attention  to  the  behavior  and  influence  of  the  zinc 
oxide  that  will  result  from  the  thorough  oxidation  of 
the  blende. 

This  substance  may  act  in  three  different  ways : 

1.  It  may  be  volatilized,  and  thus  be  removed  from 
the  smelting  zone  altogether ;  forming  accretions  on  the 
furnace  walls,  condensing  in  the  dust-chambers,  or  es- 
caping into  the  atmosphere. 

2.  It  may  be  dissolved  in  the  slag  as  zinc  oxide,  with- 
out combining  with  silica. 

3.  It  may  enter  the  slag  as  a  silicate,  or,  perhaps,  as 
an  aluminate  or  ferrate. 

The  first  of  these  three  conditions  usually  prevails 
where  the  percentage  of  blende  in  the  charge  is  not  ex- 
cessive (perhaps  6  or  7  per  cent),  and  where  the  ratio  of 
concentration  is  high,  owing  to  powerful  and  prolonged 
oxidation.  This  always  means  a  highly  silicious  or  alum- 
inous slag,  and  a  comparatively  slow  sinking  of  the 
charge.  The  zinc  is  exposed,  before  it  reaches  the 
smelting  zone,  to  such  a  high  and  prolonged  oxidizing 
temperature,  that  it  is  completely  decomposed  and  vol- 
atilized. 

The  second  and  third^  alternatives  may  be  considered 
together.  These  include  the  cases  in  which  the  zinc 
oxide,  in  part,  enters  the  slag,  but  whether  in  simple  so- 
lution, or  as  a  zinc  silicate,  is  not,  so  far  as  I  am  aware, 
definitely  settled.  At  any  rate,  this  is  not  the  place  to 
discuss  such  a  point,  and,  while  the  distinction  is  one  of 
a  good  deal  of  importance  to  the  practical  metallurgist, 
we  must  be  content  to  hold  the  matter  in  abeyance  for 
the  present,  and  confine  ourselves  to  studying  the  ef- 
fects which  zinc  oxide  produces  when  it  enters  the  slag, 
whether  it  be  there  in  solution,  or  whether  in  combina- 
tion with  the  silica  or  other  acid  constituents. 

170 


E.  D.  PETERS. 

Austin  says  that  zinc,  up  to  10  per  cent  of  the  charge, 
is  treated  successfully,  but  calls  attention  to  the  fact 
that,  in  the  presence  of  much  alumina,  it  causes  trouble. 

Bretherton,  who  has  unusual  experience  on  this  par- 
ticular point,  and  is,  at  present,  smeltingizinky  ores  with 
a  high  ratio  of  concentration,  a  silicious  slag,  a  mini- 
mum of  coke,  and  a  product  that  has  to  be  free  from 
zinc  to  escape  penalization  by  the  refiners,  says :  "I  do 
not  think  it  advisable  to  make  a  slag  containing  more 
than  12  per  cent  zinc;  that  is,  15  per  cent  zinc  oxide, 
and  the  ferrous  oxide  must  be  reduced  in  proportion. 
So  that  for  practical  running,  I  would  put  the  maximum 
amount  of  zinc  oxide  at  n  per  cent,  and  the  minimum 
amount  of  lime  at  10  per  cent,  assuming  that  there  is  no 
magnesia  nor  alkaline  bases  in  the  slag." 

Lloyd,  referring  to  reverberr.tory,  rather  than  pyrite, 
smelting,  says :  "My  personal  experience  with  zinky 
slags  has  been  more  through  reverberatory  practice 
than  blast-furnace  practice,  and  I  have  noted  that  zinky 
slag  in  a  reverberatory,  that  is,  a  slag  exceeding  10  per 
cent  ZnO,  while  it  never  becomes  as  liquid  as  a  slag 
containing  an  equivalent  amount  of  silica,  but  with  FeO 
as  practically  its  only  base,  still  smelts  at  quite  as  low 
a  temperature,  and,  as  far  as  copper  is  concerned,  is 
quite  as  clean.  ,1  should  say  that  ZnO  has  not  so  much 
the  effect  of  lowering  the  fusing  point,  as  of  thickening 
the  slag." 

Nutting  says :  "This  element,  in  the  form  of  sulphide, 
is  an  unmitigated  nuisance.  Its  bad  effects  are  numer- 
ous, and  will  be  noted  in  the  tonnage,  recovery,  and 
product ;  difficulties  start  with  as  little  as  three  per  cent 
in  the  charge,  and  increase  quite  in  proportion  until 
twelve  per  cent  is  reached,  when  the  bad  effects  be- 
come serious." 

In  the  light  of  Mr.  Nutting's  reply,  we  may  consider 
the  unfortunate  behavior  of  zinc  blende  in  that  class  of 
cases  where  considerable  heavy  sulphides  are  present 

171 


PYRITE    SMELTING. 

where  the  slag  is  not  very  silicious,  and  where  the  ratio 
of  concentration  is  not  high.  Undei  such  circumstances 
we  do  not  have  the  prolonged  and  tremendous  oxida- 
tion at  a  high  temperature  that  I  have  referred  to  in  a 
former  paragraph.  A  certain  proportion  of  the  blende 
escapes  oxidation,  enters  the  matte  and  slag,  and  pro- 
duces the  disagreeable  results  so  familiar  tc  all  of  us. 
I  do  not  at  all  wish  to  imply  that  it  would  be  more  ad- 
vantageous for  Mr.  Nutting  to  form  a  more  silicious 
slag,  increase  his  oxidation  and  his  ratio  of  concentra- 
tion, and  burn  all  his  blende  to  oxide  before  it  reaches 
the  smelting  zone.  I  have  very  little  doubt,  that  he  is 
pursuing  the  method  best  calculated  for  paying  divi- 
dends, and  refer  merely  to  the  chemical,  and  not  the 
commercial,  features  of  his  difficult  ores. 

Both  Godshall  and  Ingalls  speak  strongly  on  this 
very  point.  They  claim  that  if  ores  contain  so  much 
zinc-blende  that,  in  smelting  them  raw,  any  consider- 
able portion  of  the  zinc  escapes  oxidation,  and  thus  en- 
ters the  molten  products  as  a  sulphide,  it  may  be  better 
to  transform  the  ZnS  into  ZnO  by  a  preliminary  roast- 
ing. I  quite  agree  with  them  on  this  point,  especially 
where  the  rate  of  concentration  is  to  be  low  and  the  ox- 
idation moderate ;  but  in  cases  where  there  is  high  con- 
centration, silicious  slag,  and  powerful  oxidation,  I 
think  that  pyrite  smelting  can  be  done  more  cheaply 
and  with  less  loss  of  values  than  roasting  and  smelting 
with  coke.  In  a  word,  I  believe  that  in  this  class  of 
cases,  we  can  roast  the  blende  more  cheaply  in  the  blast 
furnace  than  we  can  outside  of  it,  besides  saving  enough 
time  and  coke  to  show  a  considerable  advantage  for  the 
pyritic  method. 

Thus  far,  we  have  no  real  conflict  of  opinion,  as  any 
differing  expression  in  the  views  of  correspondents  has 
arisen  from  the  fact  that  'pyrite'  smelting  covers  such  a 
wide  field,  that  it  embraces  conditions  under  which  it 
can  advantageously  treat  ores  high  in  zinc-blende,  as 

172 


p.  D.  PETERS. 

well  as  conditions  under  which  it  would  make  a  Door 
showing  on  ores  containing  a  similar  proportion  of  that 
mineral. 

There  is  one  single  point,  however,  on  which  Mr. 
Bretherton  differs  radically  both  from  Mr.  Godshall 
and  Mr.  Ingalls.  Bretherton  places  the  maximum 
amount  of  ZnO  that  the  slag  may  contain  at  15  per  cent, 
and  says  that  the  FeO  should  be  reduced  proportion- 
ately, while  there  should  be  a  minimum  amount  of  10 
per  cent  of  CaO  or  equivalent  earthy  bases.  He  does 
not  mention  any  reduction  in  silica ;  so  we  may  assume 
that  he  finds  it  practicable  to  run  with  his  normal,  rather 
silicious  slag,  even  when  a  pretty  high  percentage  o£ 
ZnO  is  present.  It  must  also  be  explained  that  Breth- 
erton's  slags  at  Val  Verde  usually  contain  8  to  12  per 
cent  alumina,  which  he  reckons  on  the  acid  side. 

Godshall  says :  "High  zinc  slags  invariably  require  a 
heavy  percentage  of  iron,  and  render,  therefore,  the 
usually  profitable,  and  always  desirable,  high  silica 
slags  an  impossibility." 

Ingalls  says  (quoting  from  the  middle  of  a  sentence) : 
"And  the  slag  must  be  high  in  iron  ...  in  order  to 
carry  off  zinc." 

Hofman,  in  referring1  to  the  slagging  of  ZnO  in  the 
lead  blast  furnace,  says:  "Care  must  be  taken  that  it 
is  not  reduced  to  metal ;  hence  the  smelting:  has  to  be 
done  quickly,  and  at  a  low  temperature.  This  requires 
a  slag  not  high  in  silica,  and  with  a  preponderance  of 
iron." 

My  own  experience  leads  me,  in  certain  cases,  to  con- 
cur in  the  views  of  the  three  last-named  authors.  But 
does  not  this  divergence  of  opinion  between  Brether- 
ton on  the  one  side,  and  Godshall,  Hofman,  and  Ingalls 
on  the  other,  arise  from  the  fact  that  the  two  opposing 
views  are  based  on  opposing  conditions? 

^'Metallurgy   of   Lead,"   page   292. 
173 


PYRITE  SMELTING. 

Only  a  few  months  ago,  I  stood  at  the  tunnel-head 
of  Bretherton's  Val  Verde  furnace,  and  saw  a  mixture 
heavy  in  zinc-blende  and  earths,  and  low  in  iron,  shov- 
eled into  the  charging-door.  The  slag  from  this  charge 
was  liquid,  and,  physically,  of  excellent  quality  to  the 
eye,  and  the  daily  analyses  showed  that  it  contained 
approximately :  Silica,  37  per  cent ;  alumina,  10  per  cent ; 
ferrous  oxide,  25  per  cent ;  lime,  16  per  cent ;  magnesia, 
2  per  cent ;  zinc  oxide,  7  per  cent ;  copper,  0.3  per  cent, 
with  silver  0.5  oz.  and  gold,  0.02  per  ton.  A  good  deal 
of  the  zinc  in  the  charge  had  been  volatilized,  and  the 
matte  contained  so  little  of  that  metal,  that  after  a  sin- 
gle concentration  smelting  of  the  matte,  the  enriched 
product  was  free  from  zinc.  Figuring  alumina  as  an 
acid,  the  above  slag  is  almost  exactly  a  bisilicate.  It 
seems  almost  certain,  therefore,  that  in  this  case,  in  the 
presence  of  a  powerful  oxidizing  atmosphere,  a  high 
temperature,  and  a  prolonged  contact  with  free  silica, 
such  of  the  ZnO  as  escapes  volatilization  combines  with 
the  silica  to  form  a  silicate  of  zinc,  and  thus  acts  dis- 
tinctly as  a  base,  permitting  a  corresponding  lessening 
of  ferrous  oxide  in  the  charge,  up  to  a  certain  limit. 

The  practical  lesson  that  we  may,  perhaps,  deduce 
from  these  observations  is,  that  the  proportion  of  blende 
that  we  can  successfully  handle  in  a  charge,  without 
producing  accretions,  foul  slags,  and  other  well  known 
difficulties,  probably  bears  a  definite  relation  to  the 
vigor  of  the  oxidation  in  our  furnace  shaft,  always  as- 
suming that  there  must  be  sufficient  free  silica  to  com- 
bine with  the  zinc  oxide  that  escapes  volatilization ;  and 
that  this  free  silica  must  be  in  excess  of  the  silica  that  it 
is  necessary  to  have  to  form  a  bisilicate  with  the  lime 
present,  and  a  singulo-silicate  with  the  ferrous  oxide  that 
will  result  from  the  iron-bearing  sulphides  or  arsenides 
that  we  intend  to  decompose.  This  proposition  is  mere- 
ly tentative,  and  for  the  purpose  of  inviting  discussion. 


174 


E.  D.  PETERS. 

7.  DEGREE  OF  DESULPHURIZATION  ATTAINABLE. 

This  question  must,  of  course,  be  interpreted  as 
meaning,  "What  is  the  degree  of  desulphurization  that 
it  is  commercially  advantageous  to  attain?"  The  aver- 
age of  the  figures  given  by  eight  out  of  the  ten  tabulated 
answers  is  76  per  cent  as  the  amount  of  sulphur  driven 
off  in  pyrite  smelting;  in  several  instances  this  is  mod- 
ified by  the  statement  that,  with  a  silicious  slag  and  slow 
smelting,  a  much  higher  degiee  of  desulphurization  is 
attainable. 

Carpenter  says  that,  at  Deadwood,  he  has  often  oxi- 
dized all  the  sulphur  in  his  charge,  making  no  matte  at 
all  (his  gold  collecting  in  iron  sows),  while  Lang  reports 
burning  off  96  per  cent  of  the  sulphur  from  a  charge 
containing  1 1  per  cent  sulphur. 

Beardsley  touches  the  keynote  of  the  question.  His 
reply1  indicates  that  almost  any  degree  of  desulphuriza- 
tion may  be  reached,  and  that  what  particular  degree  of 
desulphurization  shall  be  attained  in  any  given  case  is 
a  commercial  proposition,  which  only  the  metallurgist 
in  charge  can  decide. 

Lang  points  out  how  greatly  the  silica  content  of  the 
slag  influences  the  expulsion  of  sulphur,  and  states  also, 
that  even  with  the  same  percentage  of  silica  in  the 
charge,  a  mixture  containing  earthy  bases,  and  espe- 
cially lime,  is  favorable  for  the  removal  of  the  sulphur. 

A  few  years  ago,  Lang  made  a  run  on  the  ores  of  the 
Blue  Dick  mine,  near  Prescott,  Arizona,  and  obtained 
such  remarkable  results  in  the  removal  of  sulphur  and 
arsenic  by  an  oxidizing  smelting  in  the  blast  furnace, 
that  it  will  be  instructive  to  refer  to  it  in  this  Review.  I 
take  the  facts  from  his  letter  published  in  the  Mining 
and  Scientific  Press  of  March  29,  1902. 

The  ore  is  a  mixture  of  quartz  and  mispickel,  con- 
taining a  little  pyrite,  chalcopyrite,  tetrahedrite,  galena, 

i  See  page  81. 

175 


PYRITE  SMELTING. 

barite,  and  spathic  iron.  The  values  are  in  gold  and  sil- 
ver. As  it  was  received  at  the  furnace,  its  approximate 
composition  was:  Silica,  45  per  cent;  iron,  17;  arsenic, 
17;  sulphur,  17;  and  copper,  0.5  per  cent.  It  was  neces- 
sary to  add  about  50  per  cent  limestone  to  form  the  re- 
quired slag.  The  circular  trial-furnace  was  36  in.  in 
diameter  at  the  tuyeres,  and  the  cast-iron  water  jackets 
were  only  30  in.  high,  the  brick  shaft  extending  to  the 
charge  door,  which  was  n  It.  above  the  tuyeres.  The 
blast  was  cold,  and  the  pressure  only  9  oz.  per  sq.  in. 
The  resulting  slag  contained :  Silica,  40  to  45  per  cent ; 
ferrous  oxide,  24  to  27 ;  and  lime,  20  to  24  per  cent.  Fif- 
ty tons  of  charge  was  smelted  per  24  hours,  being  over 
7  tons  per  sq.  ft.  of  hearth  area ;  a  most  extraordinary 
record  for  a  small  furnace  run  with  cold  blast,  light 
pressure,  and  an  acid  slag;  and  due,  in  great  part,  to 
the  unusual  proportion  of  volatile  constituents  in  the 
stock.  The  rate  of  concentration  was  still  more  re- 
markable when  one  recollects  that  the  ore  contained 
34  per  cent  sulphur  and  arsenic,  being  27  tons  of  ore 
into  I  ton  of  matte ;  and  this  matte  was  free  from  ar- 
senic, though  not  sufficient  in  quantity  to  entirely 
cleanse  the  slags  from  silver. 

Mr.  Lang  himself  was  evidently  surprised  at  this 
unique  result.  He  says:  "As  one-half  of  the  ore  con- 
sists of  combustible  matters  (the  iron  sulpho-arsenides 
and  sulphides),  it  appears  that  the  decomposition  was 
very  extensive.  Nearly  90  per  cent  of  the  iron  was  oxi- 
dized and  slagged  off.  Fifteen-sixteenths  of  the  sulphur 
went  up  the  chimney  or  into  the  slag ;  while  all  the  ar- 
senic was  volatilized  in  some  form  or  other.  Vast  quan- 
tities of  deep  yellow  or  red  sulphide  of  arsenic,  presum- 
ably orpiment,  passed  out  of  the  smokestack,  succeeded 
by  thick  masses  of  pearl  gray  fumes  containing  arsen- 
ious  oxide,  etc.  A  good  deal  of  metallic  arsenic  also  is 
sublimed,  but  this  speedily  becomes  oxidized,  and  per- 
meates the  atmosphere  as  gray  smoke.  Not  a  single 

176 


E.  D.  PETERS. 

particle  of  speiss  or  any  other  indication  of  arsenic  ap- 
peared at  the  bottom  of  the  furnace.  The  matte  pre- 
sents no  peculiarities  except  its  brittleness,  arising,  I 
presume,  from  the  absence  of  metallic  iron,  due  to  the 
highly  oxidizing  action  of  the  blast.  It  carries  about 
10  per  cent  copper,  which  is  not  enough  for  a  clean  sav- 
ing of  the  silver.  Measures  are  being  taken  to  procure  a 
quantity  of  copper-bearing  ores  for  admixture,  so  as  to 
bring  the  copper  contents  of  the  matte  up  to  25  or  30 
per  cent,  which  will  produce  a  cleaner  separation  of  the 
silver." 

Lang  does  not  ascribe  these  results  entirely  to  the 
oxidizing  effects  of  the  smelting,  but  believes  that  there 
happened  to  be  a  peculiarly  favorable  ratio  between  the 
proportions  of  sulphur  and  arsenic  in  the  ore,  which  in- 
duced the  extensive  sublimation  of  these  volatile  sub- 
stances, leaving  the  iron  a  prey  to  the  oxygen  of  the 
blast.  Such  reactions  as  these  furnish  food  for  reflec- 
tion and  further  experimentation. 

Lloyd  says:  "On  Butte  ores,  with  cold  blast,  75  to 
80  per  cent  desulphurization  is  obtainable." 

Mathewson  says :  "The  degree  of  desulphurization 
attainable  on  pyrite  is  80  per  cent  with  the  Butte  ores ; 
we  readily  get  75  per  cent." 

The  smelting  charge  usually  contains  much  of  its 
sulphur  in  the  shape  of  pyrite  (FeS2) ;  and,  as  pyrite 
loses  one  of  its  two  atoms  of  sulphur  long  before  the 
period  of  fusion  begins,  it  is  evident  that  we  shall  re- 
move 50  per  cent  of  this  sulphur  even  before  we  have 
to  begin  to  consider  what  else  we  must  do  to  effect  our 
desired  degree  of  concentration.  Assuming  that  the 
charge  has  sunk  to  such  a  depth  in  the  furnace-shaft 
that  this  feeble  second  atom  of  sulphur  belonging  to 
the  pyrite  has  been  sublimated,  we  have  then  left  only 
the  stable  sulphides,  such  as  FeS,  Fe2S3,  Cu2S, 
PbS,  ZnS,  Ag2S,  NiS,  etc.  These  stable  sulphides  are 
not  further  decomposed  by  heat  alone,  and  will  surely 

177 


PYRITE  SMELTING. 

melt  down  into  matte  unless  they  can  be  brought  into 
contact  with  oxygen,  and  it  is  this  point  that  mainly 
distinguishes  pyrite  smelting.  Unless  so  little  coke,  or 
so  much  blast,  is  used  that  there  is  always  an  excess  of 
oxygen  beyond  the  amount  required  to  unite  with  the 
carbon  of  the  fuel,  there  will  be  no  oxidizing  effect, 
and,  consequently,  no  pyrite  smelting.  Even  if  there  be 
an  excess  of  air  blown  in,  there  will  be  but  unsatisfac- 
tory oxidation  of  these  stable  sulphides,  unless  free 
silica  be  also  furnished  to  combine  with  the  ferrous 
oxide  set  free  by  the  decomposition  of  the  pyrite. 

Consequently,  in  studying  pyrite  smelting,  we  invari- 
ably get  back  to  the  two  foundation  stones  of  the  fabric 
— abundant  oxygen,  and  free  silica. 

Since  writing  the  foregoing,  I  have  received  a  letter 
from  Mr.  Bretherton,  of  the  Val  Verde  smelter,  which 
contains  the  description  of  a  little  metallurgical  incident 
so  instructive,  and  bearing  so  exactly  upon  the  present 
question,  that  I  quote  it  herewith :  "I  want  to  mention 
a  little  experience  that  we  had  here  just  before  the  close 
of  our  last  run.  I  had  put  on  a  charge  figured  at  47 
per  cent  silica,  supposing  that  the  ore  I  was  using,  as 
unloaded,  would  assay  60  per  cent  silica ;  and  expected 
to  make  a  20  per  cent  copper  matte.  I  had  instructed 
the  feeders  to  carry  the  furnace  very  low.  The  furnace 
ran  very  slowly ;  the  matte,  instead  of  assaying  20  per 
cent  copper,  which  would  have  made  a  concentration  of 
nearly  ten  to  one,  assayed. 33  per  cent  for  two  shifts. 
When  I  came  to  get  the  true  analysis  of  the  ore,  I  found 
that  my  silicious  ore  contained  74  per  cent  silica,  which 
would  have  given  me  nearly  55  per  cent  silica  in  the 
slag,  if  it  had  not  been  that  the  slow  running  and  high 
concentration  forced  into  the  slag  the  iron  which  would 
otherwise  have  gone  into  the  matte ;  but,  by  running  a 
very  low  charge,  a  regular  scorifying  action  took  place. 
As  it  was,  my  slag  contained  48  per  cent  of  acid;  just 
enough  below  the  bisilicate  line  to  flow  nicely."  Truly, 

178 


E.  D.  PETERS. 

in  the  words  of  Dr.  Carpenter,  "The  pyritic  furnace 
chooses  its  own  slag." 

The  heavy  tonnage  and  powerful  desulphurization 
obtained  at  the  Boundary  Gmelters  in  British  Columbia, 
at  Butte,  at  Mount  Lyell  in  Tasmania,  and  at  the  Ten- 
nessee Copper  Company's  smelter  near  Ducktown, 
show  that  it  is  a  powerful  blast  (whether  hot  or  cold) 
that  is  needed,  and  that,  in  addition,  the  slag  must  be 
somewhat  silicious  if  reasonable  desulphurization  is  de- 
sired. The  cases  in  which  a  heated  blast  seems  almost 
indispensable  are  those  in  which  the  sulphides  (heat-pro- 
ducers) are  comparatively  scarce,  the  earthy  bases 
abundant,  the  slag  silicious,  and  the  ratio  of  concentra- 
tion high.  In  such  cases,  the  metallurgist  cannot  use 
sufficient  coke  to  supply  the  heat  required  to  complete 
the  fusion,  without  interfering  with  his  oxidizing  atmo- 
sphere, and  thus  spoiling  his  concentration;  and  it  is 
for  the  purpose  of  furnishing  these  few  units  of  heat 
that  are  lacking  that  the  heated  blast  is  essential. 

It  seems  to  me,  therefore,  that,  while  we  have  no 
sufficient  evidence  to  prove  that  a  heated  blast  has  any 
more  direct  effect  than  a  cold  blast  in  producing  the 
oxidizing  influence  necessary  to  a  high  degree  of  con- 
centration, it  has  an  indirect  effect  of  such  importance 
that,  with  certain  ores,  it  renders  a  degree  of  concentra- 
tion possible  that,  with  a  '-old  blast,  would  be  impos- 
sible. This  matter  has  also  been  discussed  under  the 
question  relating  to  the  use  of  hot  blast.  In  summing 
up,  it  may  be  said  that,  while  almost  any  degree  of  de- 
sulphurization is  obtainable  in  the  pyrite  furnace  with 
suitable  ores  and  ample  heated  blast,  the  average  result 
thus  far  in  practice  is  the  removal  of  about  75  per  cent 
of  the  sulphur,  and  that  local  conditions  must,  in  each 
case,  determine  how  much  beyond  this  it  is  profitable 
to  go. 


179 


PYR-1TE    SMELTING. 


8,  9,  and  10.     RELATIVE  CAPACITY  AND  ECONOMY. 

This  phase  of  the  subject  has  already  been  partially 
considered  in  article  No.  i,  which  treats  of  the  types  of 
ores  suited  to  the  process. 

The  replies  to  the  question  involving  the  economy  of 
pyrite  smelting  are  all  highly  favorable.  This  is  quite 
natural,  as  these  replies,  without  exception,  come  from 
men  who  are  pyrite  smelters,  and  who  would  not  be 
practicing  this  method  if  they  did  not  find  it  advan- 
tageous. 

This  closing  article,  therefore,  is  primarily  addressed 
to  those  members  of  the  profession  who  are  not  prac- 
tically familiar  with  pyrite  smelting. 

There  is  no  metallurgist  in  the  world  so  situated  that 
he  would  not  gladly  save  fuel  in  smelting.  The  great 
majority  of  smelters  would  thankfully  avoid  a  prelim- 
inary roasting  of  their  ores,  with  its  expensive  plant,  and 
its  attendant  cost,  delay  and  loss.  The  ability  to  pro- 
duce a  slag  containing  5  to  12  per  cent  more  silica  than 
is  practicable  by  the  ordinary  method  would  be  a  great 
boon  to  nine  smelters  out  of  ten. 

When,  however,  a  method  of  gaining  these  several 
important  advantages  simultaneously  is  offered  to  a 
metallurgist,  and  he  is  assured  that  he  can  enjoy  them 
all  without  making  any  important  alterations  in  his 
works,  and  by  merely  shutting  down  his  roasting  plant 
and  feeding  less  coke  into  his  blast  furnace,  he  feels, 
very  naturally,  a  strong  suspicion  that,  to  obtain  such 
manifold  and  striking  benefits,  without  attendant  draw- 
backs, is  too  much  to  hope  for.  Sudden  and  radical 
alterations  of  either  principles  or  practice  are  disliked 
by  the  experienced  smelter. 

I  know,  from  my  private  correspondence,  that  many 
able  men  are  startled  by  the  results  obtained,  for  in- 
stance, by  Beardsley  and  Sticht  in  smelting  the  pyritic 

180 


E.  D.  PETERS. 

ores  of  Mt.  Lyell  with  0.5  per  cent  of  coke  and  a  cold 
blast,  and  making  concentration  of  seven  into  one;  or 
by  Bretherton's  running  on  a  silicious  charge  of  raw 
zinc,  lead,  antimony,  and  arsenic-bearing  ores,  and  con- 
centrating fifteen  into  one  with  less  than  5  per  cent  of 
bad  coke,  and  an  almost  complete  elimination  of  the  im- 
purities just  mentioned. 

It  must  be  borne  in  mind  that  such  results  as  these  are 
the  fruit  of  years  of  experience,  experiment  and  ex- 
pense, and  cannot  be  immediately  duplicated  in  a  new 
enterprise,  and  especially  not  by  metallurgists  who  lack 
a  long  apprenticeship  before  the  pyrite  furnace. 

There  is,  however,  a  wide  and  fruitful  territory  lying 
between  the  two  extremes  of  blast-furnace  practice — • 
that  is  to  say,  between  the  common  roasting  and  reduc- 
tion smelting  of  copper  ores  on  the  one  hand,  and  the 
most  advanced  type  of  pyrite  smelting  on  the  other; 
and  it  is  quite  practicable  for  the  conservative  metallur- 
gist to  feel  his  way  cautiously  along  the  newer  line  of 
practice  without  materially  altering  his  plant,  and  with- 
out losing  touch  with  the  old  method  which  he  thor- 
oughly understands. 

No  metallurgist  would  feel  that  he  was  taking  any 
serious  risks  in  making  the  three  following  slight  modi- 
fications in  his  blast  furnace  practice : 

1.  Using  some  rather  poorly  roasted  ore. 

2.  Lowering  the  ore  column  in  the  furnace. 

3.  Increasing  the  silica  contents  of  the  charge  by  a 
few  per  cent. 

Under  proper  conditions,  he  would  then  find  that  he 
was  producing  a  matte  of  about  the  same  grade  as  by 
his  ordinary  method,  and  that,  consequently,  he  was 
burning  off  more  of  the  sulphur  in  the  blast  furnace  and 
oxidizing  more  of  the  iron  than  usual ;  and  that  his  fur- 
nace was  smelting  rather  more  slowly  than  before,  in 
consequence  of  the  more  silicious  slag. 

181 


PYRITE  SMELTING. 

This  is  the  beginning  of  pyrite  smelting,  and  I  ob- 
tained my  first  clear  ideas  of  it  many  years  ago  from 
Bartlett's  work  at  his  small  smelter  in  Portland,  Maine. 

Very  little  financial  advantage  is  obtained  by  this 
method  of  running  a  furnace.  There  is  a  saving  in  roast- 
ing, as  poorly  roasted  ore  can  be  used  in  the  blast  fur- 
nace ;  there  is,  also,  usually  a  decided  advantage  in  being 
able  to  employ  a  more  silicious  charge.  There  is,  gen- 
erally, no  saving  in  coke,  owing  to  the  more  refractory 
slag  and  the  low  ore  column,  which  offset  the  heat  de- 
rived from  the  decomposition  of  the  sulphides  in  the 
charge. 

As  the  furnace  men  become  familiar  with  the  new 
method  of  working,  further  changes  can  be  made.  The 
ore  column  is  gradually  restored  to  its  full  height,  and 
the  necessary  strong  oxidizing  effect  is  maintained  by 
increasing  the  blast.  The  coke  is  gradually  diminished 
and  the  proportion  of  raw  sulphide  ores  increased,  the 
ratio  of  concentration  being  regulated  mainly  by  the 
silica  contents  of  the  charge. 

It  cannot  be  too  often  repeated  that  there  will  be 
little  oxidizing  effect  and  little  concentration  until  the 
silica  of  the  charge  is  provided  as  follows: 

a.  Sufficient  silica  to  form  a  bisilicate  with  the  lime 
and  magnesia. 

b.  Sufficient  silica  to  form  a  singulo-silicate  with  any 
oxidized  iron  or  manganese  that  the  charge  may  con- 
tain. 

c.  Sufficient  silica  to   combine  as  a  singfulo-silicate 
with  the  ferrous  oxide  that  will  be  produced  by  the  ox- 
idation of  sufficient  of  the  pyrite  present  to  leave  only 
enough  sulphides  to  produce  a  matte  of  the  desired 
grade. 

The  total  silica,  therefore,  that  must  be  present  in  the 
charge  will  be  a+b+c,  a+b  representing  the  silica  that  is 
already  neutralized  by  the  oxidized  bases  present  in  the 

182 


E.  D.  PETERS. 

original  charge,  while  c  represents  the  excess  of  free 
silica  that  is  unprovided  for,  and  that  lies  waiting  un- 
fused,  and  delays  the  smelting  operation  until  sufficient 
pyrite  is  decomposed  by  the  blast  to  furnish  the  ferrous 
oxide  that  is  required  to  satisfy  this  silica  to  the  degree 
of  singulo-silicate. 

It  is  this  delaying  and  holding  back  of  the  operation 
by  the  excess  of  free  silica  that  makes  pyrite  smelting, 
other  conditions  being  equal,  a  decidedly  slower  process 
than  the  simple  fusion  of  an  already  oxidized  charge. 
If  there  were  no  free  silica  present,  the  sulphides  would 
simply  melt  down  with  great  ease  and  rapidity  into  a 
low-grade  matte,  as  so  frequently  occurred  in  the  early 
days  of  raw  smelting  of  heavy  sulphide  ores  with  too 
basic  a  slag.  It  follows,  consequently,  that  this  excess 
of  free  silica  is  an  essential  portion  of  the  pyrite  charge, 
and  the  delay  that  it  caused  by  holding  up  the  process 
until  sufficient  pyrite  had  been  oxidized  to  furnish  it  with 
FeO  has  been  obviated  by  heightening  the  ore  column 
and  greatly  increasing  the  pressure  and  volume  of  the 
blast.  The  decomposition  of  the  pyrite  that,  with  the 
light  blast,  progressed  slowly  and  reduced  the  capacity 
of  the  furnace  much  below  the  normal  duty  of  a  furnace 
of  similar  hearth  area  running  on  roasted  ore  and  coke, 
now,  with  a  heavy  blast,  proceeds  with  rapidity. 

The  economy  of  a  smelting  process  stands,  to  some 
considerable  extent,  in  relation  to  the  capacity  of  the 
furnace  employing  that  process.  Owing  to  Beardsley's 
vakiable  communications  to  the  Journal,1  we  have  some 
quite  exact  information  as  to  the  capacity  of  furnaces  at 
the  Mt.  Lyell  smelter,  which  employs  genuine  pyrite 
smelting,  and  makes  a  concentration  on  heavy  pyrite 
ore  of  about  seven  to  one  on  the  first  fusion. 

A  furnace  210  in.  by  42  in.  with  a  cold-blast  pressure 
of  20  to  30  oz.  per  square  inch,  averaged  271.43  tons  of 
charge  per  24  hours,  which  is  4.42  tons  per  square  foot 

iBee  pp.  81  and  219  of  this  work. 

183 


PYRITE    SMELTING. 

of  hearth  area.  The  same  furnace,  with  a  blast  pressure 
of  40  to  45  oz.,  averaged  530.76  tons  of  charge  per  24 
hours,  which  is  8.65  tons  per  square  foot  of  hearth  area. 
Thus  the  capacity  of  the  furnace  was  nearly  doubled  by 
an  increase4  in  blast  pressure  of  some  20  oz.  per  square 
inch,  and  its  duty  per  square  foot  of  hearth  area  was 
brought  up  close  to  the  highest  average  record  of  any 
of  the  large  blast  furnaces  running  on  roasted  ore. 

The  interesting  results  obtained  by  W.  H.  Freeland 
on  the  pyrrhotite  ores  of  Ducktown,  Tennessee,  demon- 
strate with  equal  conclusiveness  that,  in  using  this  meth- 
od on  heavy  sulphide  ores,  a  cold  blast  gives  entirely 
satisfactory  results,  providing  there  is  enough  of  it,  and 
that  the  capacity  of  the  furnace  depends  largely  upon  the 
volume  and  pressure  of  this  blast.  The  pyrite  furnace 
demands  a  much  larger  blowing  plant  than  does  a  fur- 
nace of  equal  capacity  running  on  roasted  ore. 

There  is  one  more  decided  disadvantage  with  which 
the  raw  smelting  method  must  be  debited.  It  is  a  very 
much  more  difficult  process  to  conduct  than  the  ordi- 
nary smelting  of  roasted  copper  ores  with  coke.  The 
chemical  and  physical  phenomena  that  accompany  the 
production  of  heat  from  the  oxidation  of  carbon  are 
simpler  and  more  manageable  than  those  that  are  in- 
volved in  the  production  of  heat  from  the  oxidation  of 
metallic  sulphides,  and  the  great  amount  of  solid  resi- 
dues from  the  combustion  of  the  latter  substances  also 
has  to  be  cared  for.  In  plain  language,  it  is  easier  to 
burn  coke  in  a  blast  furnace  than  it  is  to  burn  pyrite. 

Consequently,  in  pyrite  smelting  the  entire  operation 
is  very  much  more  delicate  and  precarious  than  when 
using  carbonaceous  fuel.  A  shutdown  of  an  hour  may 
affect  the  behavior  of  the  furnace  for  the  succeeding  one 
or  two  shifts ;  great  skill  and  watchfulness  are  necessary 
on  the  part  of  both  metallurgist  and  furnacemen,  and 
campaigns  are  seldom  very  long. 

184 


E.  D.  PETERS. 

SUMMARY  OF  RESULTS. 

A  rough  balance  sheet  may  serve  to  bring  out  the 
principal  pros  and  cons  more  clearly,  it  being  under- 
stood that  it  applies  solely  to  heavy  pyritic  ores. 

Pyrite  Process — Advantages. 

1.  No  roasting  required.     (Saving  in  plant,  in  costs, 
in  losses  of  metal,  in  time.) 

2.  Great  saving  in  coke. 

3.  More  silica  can  be  used  in  charge. 

4.  More  complete  elimination  of  Pb,  As  and  Sb. 

5.  Heavy   spar  less  objectionable  than  in   ordinary 
smelting. 

Pyrite  Process — Drawbacks. 

1.  Heavier  blast. 

2.  Exceptional  care  and  skill. 

3.  Shorter  campaigns. 

4.  Possible  reconcentration  of  matte. 

5.  Zinc  more  injurious  than  with  a  roasted  charge. 

6.  Sulphur  fumes  are  wasted. 

Local  conditions  must  decide  on  which  side  the  bal- 
ance of  profit  lies.  In  the  majority  of  cases  the  pyrite 
process  will  be  found  the  more  economical  on  the  heavy 
sulphide  ores  that  we  are  now  considering.  The  cost  of 
fuel  is  the  greatest  item  of  expense  in  ordinary  blast 
furnace  smelting,  and  a  method  that  promises  a  saving 
of  one-half  to  nine-tenths  of  this  costly  material  is  en- 
titled to  the  most  serious  consideration. 

If  the  smelter  is  so  situated  that  the  sulphur  dioxide 
derived  from  the  roasting  of  the  ores  can  be  used  for 
the  manufacture  of  acid,  it  becomes  a  question  whether 
the  profit  derived  from  making  acid  is  greater  than  the 
gain  that  will  arise  from  diminishing  the  coke.  It  may, 
perhaps,  be  found  feasible  to  employ  the  fumes  from  the 
pyrite  smelter  direct  for  the  manufacture  of  sulphuric 

185 


PYRITE  SMELTING. 

acid.    Beardsley  finds  that  the  gases  from  the  Mt.  Lyell 
blast  furnaces  contain  little  or  no  free  oxygen. 

The  concentration-smelting  of  a  low-grade  matte  up 
to  a  point  suitable  for  the  converters  is  not  so  serious  a 
matter  as  is  sometimes  believed  by  metallurgists  who 
have  not  had  occasion  to  practice  it  under  proper  con- 
ditions. The  simple  fusion  of  matte  in  the  blast  furnace 
(even  with  the  smallest  possible  addition  of  coke)  is  a 
waste  of  time,  unless  the  proper  chemical  reagents  are 
supplied  to  the  charge.  It  comes  out  in  very  much  the 
same  condition  as  it  went  in.  The  average  enrichment 
of  a  50  per  cent  matte  for  one  year's  work  of  the  former 
re-melting  cupola  at  the  Parrot  converter  plant  at  Butte 
was  only  about  3  per  cent  copper,  and  a  considerable 
proportion  of  this  gain  was  due  to  the  elimination  of  the 
slag  that  was  adherent  to  the  matte  when  it  came  to  the 
cupola. 

The  reagents  that  must  be  supplied  in  order  to  effect 
a  concentration  of  the  matte  are,  of  course,  oxygen  and 
free  silica,  and,  with  their  aid,  a  low-grade  copper  matte 
may  be  enriched  to  50  per  cent,  or  more,  with  certainty 
and  economy,  and  with  but  a  small  cost  per  ton  of  orig- 
inal ore.  As  this  subject  of  matte  concentration  seems 
to  be  regarded,  in  the  profession,  with  a  certain  amount 
of  suspicion,  I  quote  from  two  authors  who  have  had 
large  experience  with  this  class  of  work.  . 

Beardsley  says  i1  "Raw-mattes,  smelted  pyritically,  can 
be  concentrated  from  2\  to  3!  into  I  without  much  diffi- 
culty; and  10  per  cent  matte  can  be  made  into  35  per 
cent  matte  and  converted  as  such ;  and  20  per  cent  matte 
can  be  raised  to  55  per  cent  matte  in  a  single  operation/* 

Freeland,  who  has  obtained  such  economical  results 
at  the  Ducktown  Sulphur,  Copper  and  Iron  Company's 
works  by  substituting  pyrite  smelting  for  the  ordinary 
roasting  and  fusion  with  coke,  says :  "The  reconcentra- 

iTfte  Engineering  and  Mining  Journal,  June  30, 1904,  p.  1035. 

186 


E.  D.  PETERS. 

tion  of  the  first  matte  (20  per  cent  matte  concentrated 
to  about  50  per  cent  copper)  presents  no  difficulties  at 
Ducktown.  There  is  no  limit,  within  the  range  of  matte, 
to  this  second  operation.  A  6  per  cent  matte  may  be 
brought  up  to  50  per  cent  quite  as  successfully  as  may 
any  higher  grade  initial  matte ;  nor  is  this  statement 
based  upon  odd  or  occasional  samples,  but  upon  more 
than  one  carload  of  matte  so  made.  The  degree  of  con- 
centration, whether  in  the  first  (raw  ore  smelting)  or 
second  (raw  matte  smelting)  operation  is,  in  the  main, 
proportionate  to  the  speed  at  which  the  furnace  is 
driven,  and  is  controlled  by  the  proportion  of  quartz  on 
charge,  or  by  the  manipulation  of  the  blast,  or  both. 
But  on  these  seemingly  simple  measures  hinges  not 
only  the  grade  of  the  matte,  but  the  life  of  the  cam- 
paign." 

The  presence  of  even  5  per  cent  of  zinc-blende  in  the 
charge  adds  materially  to  the  difficulties  encountered  in 
the  raw  smelting  of  heavy  sulphide  ores.  Nutting 
speaks  strongly  regarding  its  injurious  effects,  and  also 
experiences  much  trouble  from  having  to  use  ores  in 
which  the  sulphides  are  mostly  in  a  finely  divided  con- 
dition. 

When  these  two  drawbacks  are  not  present  in  an  ag- 
gravated form,  it  seems  probable  that  heavy  pyrite  ores 
can  usually  be  smelted  raw  with  cold  blast  more  eco- 
nomically, and  with  less  loss  of  metal,  than  by  the  or- 
dinary method,  and  that  even  the  necessity  of  a  concen- 
tration-smelting of  the  first  matte,  to  raise  it  to  the 
proper  grade  for  the  converters,  will  not  outweigh  the 
advantages  of  the  pyrite  method. 

As  raw  smelting  demands  a  more  silicious  slag  than 
ordinary  smelting,  it  follows  that  when  the  charge  is  a 
basic  one,  and  no  silicious  ores  are  available  (as  at  Duck- 
town),  more  barren  quartz  must  be  added  than  in  ordi- 
nary smelting.  We  know  also  that  the  pyrite  furnace  re- 
quires a  powerful  blast,  and  if,  in  addition,  the  price  of 

187 


PYR1TE    SMELTING. 

coke  is  low,  wages  are  light,  and  climate  and  conditions 
are  suitable  for  heap-roasting,  I  can  well  imagine  that 
the  ordinary  roasting  and  smelting  might  be  the  more 
advantageous  of  the  two.  If,  however,  any  of  the  above 
advantages  are  lacking,  it  does  not  seem  probable  that 
it  can  compete  with  pyrite  smelting;  while  if  coke  and 
labor  are  tolerably  expensive,  and  the  climate  too  wet 
for  advantageous  heap-roasting,  there  can  be  no  ques- 
tion as  to  greater  economy  of  the  newer  method.  If,  in 
addition,  there  is  an  available  supply  of  profitable  sili- 
cious  ore,  the  raw  method  shows  up  to  still  greater  ad- 
vantage. 

Since  the  Mt.  Lyell  Company  has  been  able  to  replace 
barren  quartz  by  a  supply  of  silicious  ore  of  good  grade 
in  copper,  and  can  thus  eliminate  worthless  flux,  and 
also  produce  at  the  first  smelting  a  matte  suitable  for 
immediate  converting,  it  has  greatly  decreased  its  Met- 
allurgical expenses.  During  the  past  half-year  it  has 
cost  the  company  only  $1.87  per  short  ton  to  smelt  its 
raw  ores  into  matte  suitable  for  converting. 

The  cost  of  producing  metallic  copper  from  the  heavy 
pyrrhotite  ores  of  the  Ducktown  Sulphur,  Copper  & 
Iron  Company,  Ltd.,  is  3.018  c.  per  pound  less  than  by 
the  former  method  of  heap-roasting  and  smelting  with 
coke.  This  statement  is  given  on  the  authority  of  the 
smelter  superintendent,  Mr.  W.  H.  Freeland,  and  if  we 
assume  (without  authority)  that  the  ore  yields  2.5  per 
cent  copper,  the  saving  effected  bv  the  use  of  the  pyritic 
method  is  $1.51  per  ton  of  ore.  The  amount  of  coke 
used  in  this  smelting  is,  I  think,  about  3  per  cent  of  the 
weight  of  the  ore,  and  the  capacity  of  the  furnace,  as  de- 
termined after  smelting  some  70,000  tons  of  ore  by  the 
new  method,  is  83.5  per  cent  of  its  former  duty  when 
smelting  roasted  ore. 

The  second  variety  of  pyrite  smelting,  which  has  been 
discussed  at  some  length  in  the  preceding  articles,  is 
characterized  by  a  comparatively  small  percentage  of 

188 


E.  D.  PETERS. 

sulphides  in  the  charge,  and  a  correspondingly  increased 
proportion  of  earthy  ingredients.  In  order  to  obtain 
the  powerful  oxidation  required  for  a  high  degree  of 
concentration,  the  coke  must  be  reduced  almost  to  the 
danger  limit,  and  the  tendency  to  chill  at  the  tuyere  zone 
is,  in  part,  counteracted  by  warming  the  blast.  The  rate 
of  concentration  is  very  high,  and  the  matte  production 
small ;  the  slag  is  silicious  to  a  degree  that  would  seem 
impossible  in  ordinary  smelting,  the  elimination  of  lead, 
zinc,  arsenic  and  antimony  extensive,  and  the  result  of 
the  slightest  irregularities  likely  to  be  serious. 

If  the  furnace  becomes  too  cold,  the  addition  of  more 
coke  is  impracticable,  as  it  would  immediately  interfere 
with  the  established  degree  of  oxidation,  and  result 
in  two  evils:  I.  An  increased  production  of  low-grade 
matte.  2.  The  consequent  robbing  of  the  slag  of  the 
iron  necessary  for  its  formation. 

I  happened  to  be  at  the  Val  Verde  smelter  just  after 
the  night  foreman  had  feared  the  furnace  was  chilling, 
and  had  added  a  very  minute  amount  of  coke  to  each 
charge  for  a  short  time.  In  a  few  hours  the  inevitable 
result  followed.  The  matte  increased  in  quantity,  and 
dropped  from  something  like  37  per  cent  copper  down 
to  30  per  cent,  and  the  slag  became  dangerously  acid. 
Bretherton  heated  up  the  furnace  and  restored  matters 
to  their  normal  condition  by  using  two  or  three  good- 
sized  charges  of -coke,  and  substituting  for  the  regular 
ore  charge  a  properly  fluxed  mixture  of  furnace  clean- 
ings, foul  slag,  etc.,  which  already  contained  its  copper 
contents  in  the  form  of  properly  concentrated  matte, 
and  possessed  sufficient  bases  to  flux  itself,  so  that  the 
powerfully  reducing  action  of  the  large  coke  charge 
could  have  no  harmful  effect  on  it,  and  merely  melted  it 
and  warmed  up  the  furnace  at  the  same  time.  Thus 
this  thin  layer  of  neutral,  and  already  sufficiently  oxi- 
dized, material  served  as  a  buffer  to  receive  without 
damage  the  reducing  action  that  was  unavoidable,  if  an 

189 


PYR1TZ  SMELTING. 

excess  of  heat  was  to  be  quickly  conveyed  to  the  lower 
portion  of  the  cold  furnace. 

As  I  have  pointed  out  in  a  previous  article,  there  is  a 
large  field  in  the  United  States  and  Mexico  (and,  doubt- 
less, in  many  other  countries)  for  this  partial  pyrite 
smelting.  The  abolition  of  a  roasting  plant,  and  the 
saving  of  from  one-half  to  four-fifths  of  the  coke,  make 
it  peculiarly  suited  to  remote  districts  where  freights  and 
fuel  are  expensive. 

The  decrease  in  depth  of  the  lead  contents  in  many 
of  the  limestone  deposits  of  the  Rocky  Mountains  and 
Mexico,  and  the  increasing  production  of  dry  silicious 
silver  and  gold  ores  carrying  only  moderate  proportions 
of  sulphide  minerals,  point  inexorably  to  the  substitu- 
tion of  matte  for  lead  as  a  collector  of  the  precious  met- 
als; and  with  the  comparatively  low  tenor  in  copper, 
and  the  general  complexity  of  the  ores  in  the  regions 
referred  to,  there  appears  to  be  no  method  yet  invented 
so  suitable  as  raw  smelting  with  a  high  degree  of  con- 
centration ;  or,  as  it  has  been  termed  in  this  review — 
'pyrite'  smelting. 

Through  close  competition  and  long  experience,  the 
lead  smelter  has  learned  that,  if  he  is  to  avoid  ruinous 
loss  of  values,  he  must  keep  his  slag  within  certain  pre- 
scribed and  narrow  limits.  It  is  not  enough  for  him  to 
hold  the  silica  contents  of  his  slag-  somewhere  between 
30  and  35  per  cent.  He  must  also  establish  and  main- 
tain a  suitable  ratio  between  the  iron  and  lime  contents 
of  the  slag,  and  this  is  a  very  expensive  thing  to  do, 
where  the  requisite  ores  do  not  exist  in  the  proper  pro- 
portions. 

It  is  here  that  the  smelter  of  roasted  copper  ore  has 
an  enormous  advantage  over  the  lead  smelter ;  in  a  gen- 
eral way  it  may  be  said  that  if  he  keeps  the  silica  in  his 
slag  somewhere  between  30  and  40  per  cent,  and  pro- 
vides ample  settling  capacity,  he  need  worry  very  little 
about  the  other  constituents  of  the  slag,  and  may  vary 

190 


E.  D.  PETERS. 

them  greatly  every  dav  without  serious  trouble.  This 
makes  the  matting  operation  a  much  simpler,  more  uni- 
versal, and  more  economical  process  than  lead  smelt- 
ing, and  fits  it  particularly  for  the  handling  of  miscel- 
laneous custom  ores  of  diverse  composition. 

The  variety  of  pyrite  smelting  that  we  are  now  con- 
sidering partakes  of  both  of  these  systems.  It  demands 
a  care  in  the  ore-mixture,  and  an  exact  determination 
of  the  composition  of  the  slag  that  is  to  be  produced, 
that  is,  at  first,  quite  irksome  to  the  ordinary  copper 
smelter.  On  the  other  hand,  it  is,  with  one  single  ex- 
ception, more  elastic  as  to  the  character  of  the  slag  that 
it  may  produce  than  any  other  smelting  operation  with 
which  I  am  familiar.  The  exception  referred  to  is,  of 
course,  the  fact  that  the  pyrite  furnace  cannot  advan- 
tageously produce  a  basic  slag.  Unless  there  is  suffi- 
cient free  silica  present  to  delay  the  smelting  until  the 
desired  amount  of  pyrite  is  oxidized  to  ensure  the 
proper  degree  of  concentration  (and,  incidentally,  to 
combine  with  the  ferrous  oxide  thus  formed),  it  will  not 
be  pyrite  smelting ;  it  will  simply  be  a  melting  down  of 
the  charge  into  a  low-grade  matte,  as  has  been  so  many 
times  insisted  upon  in  this  review. 

However,  in  the  variety  of  pyrite  smelting  that  I  am 
now  considering,  this  inability  to  produce  a  basic  slag 
will  very  seldom  prove  an  injury.  This  kind  of  pyrite 
smelting  deals  mainly  with  dry  silicious  ores,  and  every 
pound  of  extra  silica  that  the  slag  will  stand  means  just 
so  much  more  profit  for  the  smelter.  Consequently, 
the  charge  is  made  up  to  contain  the  maximum  amount 
of  silica  that  it  can  carry,  and  still  melt  at  a  temperature 
that  can  be  produced  economically  in  the  furnace.  The 
metallurgist  constantly  hovers  near  the  danger  limit, 
and,  on  the  whole,  finds  his  most  convenient  guide  not 
in  the  per  cent  of  silica  that  his  slag  contains,  but  in  the 
oxygen  ratio  between  the  basic  and  acid  constituents 
of  the  slag. 

191 


PYR1TE    SMELTING. 

Dr.  Carpenter  in  his  daring-  and  successful  inaugura- 
tion of  the  Deadwood  &  Delaware  Smelter,  in  South 
Dakota,  relied  mainly  upon  this  ratio,  and  found  it  a 
safe  guide.  He  points  out1  that  if  the  slag  is  kept  be- 
between  4RO,  3SiO2  and  RO,  SiO2— that  is  to  say,  be- 
tween a  sesquisilicate  and  a  bisilicate — it  will  generally 
be  satisfactory,  alumina  being  figured  as  a  base. 
Bftetherton,  with  a  much  higher  per  cent  of  alumina  in 
his  ores,  finds  that  he  must  figure  this  substance  on  the 
acid  side,  giving  it,  however,  something  like  two-thirds 
the  replacing  value  of  silica. 

This  is,  however,  only  one  of  the  two  points  which 
determine  the  proper  constitution  of  the  slag.  The 
second  point  to  consider  is  whether — even  though  the 
proper  ratio  between  base  and  acid  exists — the  bases 
are  of  such  a  nature  that  the  slag  will  melt  at  a  suit- 
able temperature.  These  matters  belong  to  the  study 
of  slags,  and  cannot  be  taken  up  in  this  review,  except 
to  point  out  that  the  presence  of  at  least  10  to  15  per 
cent  of  ferrous  or  manganous  oxide  is  indispensable. 

Where  proper  knowledge  and  experience  are  avail- 
able, this  partial  pyrite  smelting  seems  to  offer  the  mo.st 
economical  outlet  for  the  vast  supply  of  low-grade 
silicious  sulphide  ores  and  pyritic  concentrates,  carry- 
ing the  precious  metals,  and  but  little  copper  or  lead, 
the  production  of  which  is  at  present  hampered  by 
treatment  charges  which  are  higher  than  a  large  pro- 
portion of  these  ores  can  bear. 


^Transactions  American  Institute  Mining  Engineers,  Vol.  XXX,  page  774. 
192 


CONTRIBUTION  BY  HIRAM  W.  HIXON. 

The  Editor : 

Sir — My  experience  with  copper  ores  does  not  agree 
with  that  gained  in  smelting  copper-nickel  ores,  and  I 
find  it  necessary  to  get  out  a  revised  creed  and  smash 
a  few  of  my  former  dogmas. 

The  difference  is  radical,  and  seems  to  depend  princi- 
pally on  the  behavior  of  copper  matte  as  compared  with 
copper-nickel  matte.  The  fusing  point  of  copper  matte 
is  much  lower  than  that  of  copper-nickel  matte,  which 
is  another  way  of  stating  that  the  freezing  point  of  cop- 
per-nickel matte  is  higher  than  copper  matte  in  propor- 
tion to  the  nickel  contents.  The  result  is  that  as  the 
nickel  increases  more  fuel  is  needed  on  the  charge,  and 
this  fuel  prevents  the  oxidation  of  sulphides  and  makes 
raw  smelting  of  nickel-copper  pyrrhotite  impossible. 
Another  feature  is  that  the  copper  matte  can  absorb  a 
greater  number  of  heat  units  in  the  smelting  and  give 
them  up  to  the  slag  without  freezing  than  can  nickel 
matte.  This  results  in  preventing  accretions  at  the  tuy- 
eres and  the  elevation  of  the  smelting  zone,  which  takes 
place  rapidly  in  the  case  of  copper-nickel  ores. 

The  behavior  of  the  settler  on  a  furnace  smelting 
copper-nickel  ores  is  equally  affected  by  this  lack  of 
heat-carrying  capacity,  and  the  tendency  of  the  walls  to 
thicken  under  conditions  that  with  copper  matte  would 
cause  a  runaway,  are  quite  remarkable  when  observed. 

It  has  been  my  experience  in  Ontario  that  a  charge  of 
copper-nickel  ores  could  not  be  smelted  with  less  than 
10  per  cent  of  coke,  and  here  we  can  run  on  5  per  cent, 
smelt  75  per  cent  of  coarse  crude  ore  and  make  35  per 
cent  matte  at  one  operation. 

193 


PYRITE    SMELTING. 

Previous  to  my  experience  here  I  had  maintained  that 
the  fairy  tales  which  were  published  about  raw  smelting 
were  without  foundation,  but  I  see  now  that  I  have  been 
to  a  great  extent  the  victim  of  my  experience.  I  believe 
that,  given  the  proper  conditions,  with  a  furnace  large 
enough,  and  blowing  engines  to  give  a  positive  delivery 
of  blast  regardless  of  pressure,  and  of  sufficient  quan- 
tity, a  furnace  may  be  driven  at  the  rate  of  500  to 
1,000  tons  per  day  on  such  ores  as  Mount  Lyell,  Ten- 
nessee Copper  Company,  or  Rio  Tinto  with  less  than  I 
per  cent  of  coke,  and  effect  a  concentration  of  5  or 
more  tons  of  ore  into  one  ton  of  matte.  Further,  that 
this  matte  may  be  concentrated,  by  re-smelting  under 
similar  conditions,  to  a  converting  grade. 

Few  men  have  the  opportunity  to  experiment  with 
conditions  of  this  magnitude,  but  I  believe  that  it  will 
be  demonstrated  that  it  is  possible  and  more  profitable 
to  handle  ores  of  this  character  in  a  two-stage  raw- 
smelting  plant,  with  cold  blast,  than  by  roasting  or  with 
hot  blast. 

It  is  only  a  year  since  I  made  a  journey  of  2,000  miles 
to  see  a  furnace  that  was  said  to  be  running  on  a  charge 
of  raw  ore  with  less  than  3  per  cent  coke.  When  I  got 
there  it  was  smelting  roasted  ore  with  10  per  cent  coke, 
and  I  returned  condemning  the  whole  story  as  a  myth. 
I  have  since  found  that  given  the  proper  conditions  it 
is  quite  possible,  and  I  hasten  to  get  on  the  band-wagon 
and  say  "me  too." 

HIRAM  W.  HIXON. 

Tezuitlan,  State  of  Puebla,  Mexico,  May  27,  1904. 


194 


CONTRIBUTION  BY  WALTER  E.  KOCH. 

The  Editor : 

Sir — Following  up  my  letter  of  April  29,  I  am  able 
now  to  give  further  results,  covering  the  test  between 
hot  and  cold  blast.  In  this  last  36-days'  run,  the  cold- 
blast  furnace  was  apathetic  and  delicate,  while  the  hot- 
blast  furnace  was  robust  and  vigorous.  My  old  4§-in. 
furnace  was  handicapped  by  leaky  tuyeres,  but  still  kept 
ahead  of  its  competitor,  which,  in  spite  of  being  petted 
and  fed  with  plenty  of  matte,  calcite  ore  and  pyrite, 
was  continually  kicking.  I  find  that  cold  blast  means 
less  ore  put  through,  more  coke,  more  flux,  more  matte 
and  a  higher  pressure  of  blast. 

The  run  covered  36  days  in  April  and  May. 

A  B 

48-in.  diam.    twin  furnaces Hot  blast  Cold  blast 

Time  of  run    36  days  36  days 

Ore  charged  per  24  hours 40  tons  33.5  tons 

Coke  charged    per  cent    of  charge 7.25  to  7.5  8.75  to  9 

Coke  charged    per  cent    of  ore 9  11.33 

Percentage  of  ore  in  charge 82  77 

Before  starting  this  run,  I  moved  the  blower  to  within 
10  ft.  of  the  cold-blast  furnace,  and  it  improved  matters 
greatly.  I  also  used  a  hot  charge  with  plenty  of  matte, 
calcite  ore  and  hot  pyrite,  giving  an  easy  charge  and 
fluid  slag,  and  under  these  conditions  the  cold  blast  did 
better.  Coke  was  very  bad  part  of  the  time — small, 
dirty  and  20  per  cent  ash.  We  have  to  stop  and  clean 
out  heavy  lime  deposits  due  to  bad  water  every  four  or 
five  weeks,  so  36  days  is  rather  a  good  run.  Our 
normal  furnace  charge  for  hot  blast  is  85  per  cent  ore, 
4.5  per  cent  matte,  4.5  per  cent  slag,  and  6  per  cent 
coke.  The  ore  contains  one-half  of  one  per  cent  copper. 


PYRITE    SMELTING. 

Slag:  SiO2,  45  Per  cent;  Fe°>  37  per  cent;  CaO,  8  per 
cent;  A12O3,  8  per  cent.  Temperature  of  blast  below 
200°  C,  never  over  this.  Concentration  during  this 
run,  17  to  i. 

WALTER  E.  KOCH. 

Santa  Maria  del  Oro,  June  3,  1904. 


CONTRIBUTION  BY  G.  F.  BEARDSLEY. 
The  Editor: 

Sir — I  had  intended  to  follow  up  my  first  contribution 
before  now.  The  following  notes  are  suggested  by  the 
reading  of  the  articles  you  have  recently  published : 

I  note  first  that  Mr.  Koch  remarks  that  "zinc  sul- 
phide is  a  very  good  fuel."  Theoretically  it  is  a  good 
heat-producer,  and  when  burned  under  proper  condi- 
tions it  will  yield  a  temperature  of  1992°  C.  In  blast- 
furnace practice,  however,  its  heat-producing  proper- 
ties are  much  obscured  by  some  other  properties  that 
it  also  possesses.  Mr.  Nutting  says  it  is  "an  unmiti- 
gated nuisance."  From  an  experience  a  few  months 
ago  with  pyritic  ore  containing  6  per  cent  of  zinc,  I  am 
prepared  to  join  the  latter  gentleman's  emphatic  con- 
demnation of  it  as  against  the  sustaining  authority  of 
Messrs.  Austin,  Bretherton  and  Lloyd. 

Mr.  Mathewson  states  "fuel  can  be  eliminated  entirely 
provided  there  is  sufficient  pyrite  in  the  ore  charge." 
Working  a  pyritic  ore  of  90  per  cent  FeS2  purity  un- 
der the  most  favorable  conditions  of  ore,  furnace  and 
blast,  and  with  steady  and  intelligent  furnace  crews, 
seven  to  nine  days  were  the  longest  campaigns  obtain- 
able without  serious  trouble.  I  think  14  days  was  the 
longest  campaign,  and  this  included  an  attempt  to  burn 
the  furnace  out  with  an  increase  of  coke  after  the  trou- 
ble had  commenced.  The  experiment  of  running  with- 
out fuel  was  kept  up  for  some  time  with  two  furnaces, 
and  the  running  was  altered  as  suggested  by  the  varying 
furnace  conditions.  It  was  fully  demonstrated  that  run- 
ning entirely  without  fuel  under  the  conditions  obtain- 
able was  neither  practical  nor  economical.  The  result 
of  the  test,  however,  was  the  determination  of  the  ex- 

197 


PYRITE    SMELTING. 

ceedingly  small  amount  of  coke  that  was  really  neces- 
sary and  the  way  in  which  it  should  be  fed  when  used 
as  a  corrective  for  certain  symptoms  indicative  of  trou- 
ble going  on  under  the  surface  of  the  charge.  As  stated 
in  my  former  article,  on  some  charge  combinations,  0.4 
per  cent  coke  was  all  that  was  required  in  a  first  smelt- 
ing. 

Again  quoting  from  the  same  authority :  "Where  the 
matte  is  too  low  grade,  by  the  raw-smelting  process, 
roasting  has  to  be  resorted  to,"  and  "matte  charged  into 
the  furnace  raw  loses  hardly  any  sulphur  in  the  smelting 
process,  as  it  merely  smelts  and  runs  through  the 
charge."  Raw  mattes,  smelted  pyritically,  can  be  con- 
centrated from  2j  to  3^  into  I  without  much  difficulty. 
Ten  per  cent  matte  can  be  made  into  35  per  cent  matte 
and  converted  as  such,  and  20  per  cent  matte  can  be 
raised  to  55  per  cent  matte  each  in  a  single  operation. 
I  note  that  Mr.  Fulton  smelts  his  matte  several  times, 
but  with  little  concentration  so  far  as  the  copper  is  con- 
cerned ;  but  his  conditions  reem  to  call  for  it. 

Mr.  Bretherton  mentions,  as  a  result  of  hot  blast, 
"brighter  tuyeres."  This  was  not  noticed  in  the 'work 
under  my  supervision,  but  rather  the  contrary.  From 
three  to  four  hours  after  blowing  in,  all  the  tuyeres  would 
become  dark  with  hot  blast  as  well  as  cold,  and  no  light 
could  be  seen  in  them  again  during  the  campaign,  un- 
less some  hot  slag  happened  to  run  down  an  air  channel 
into  a  tuyere.  The  blast  entering  the  furnace  and  meet- 
ing the  down-coming  slag  robs  it  of  a  part  of  its  heat 
and  produces  a  chill  over  the  tuyeres  of  greater  or  less 
thickness,  permeated  by  irregular  air  channels.  Before 
iron,  sulphur  and  the  oxygen  of  the  air  can  unite  they 
must  be  heated  to  their  combining  temperature.  In  the 
case  of  the  air  it  can  get  only  the  additional  heat  be- 
tween the  temperature  it  has  when  sent  into  the  furnace 
and  the  combining  temperature  from  the  chill  over  the 

198 


G.  F.  BEARDSLEY. 

tuyeres  kept  hot  by  the  down-coming  slag  and  matte 
running  over  it.  This  chill  is  an  interior  hot-blast  stove 
in  effect,  and  the  endeavor  to  keep  the  tuyeres  bright 
in  many  cases  is  costing  more  coke  than  is  actually  nec- 
essary. 

The  slag  in  pyrite  smelting  begins  to  run  down 
through  the  charge  at  a  heat  but  little  above  the  forma- 
tion temperature,  and  there  can  be  but  little  superheat- 
ing, so  to  speak,  as  the  heat  liberated  by  the  rapid  oxi- 
dation of  the  sulphur  and  iron  is  carried  away  both  by 
the  matte  and  the  slag  as  fast  as  generated.  In  the  en- 
tire absence  of  coke,  the  blast,  to  gain  its  heat,  abstracts 
it  from  the  slag  in  immediate  contact  with  the  chill, 
thereby  adding  to  it  and  forcing  the  smelting  zone 
higher  and  higher,  until  finally  the  charge  smelts  on  the 
top  and  the  furnace  goes  out.  Hot  blast  will  retard  the 
growth  of  this  tuyere  chill,  but  will  not  prevent  it.  The 
quantity  of  coke  required,  therefore,  seems  to  be  an 
amount  necessary  to  counteract  the  chilling  effect  of  the 
incoming  blast  upon  the  descending  low-temperature 
slag  and  to  establish  a  balance  which  shall  keep  the 
smelting  zone  in  its  proper  place. 

Mr.  Bretherton  further  remarks,  "hot  blast  reduces 
cost  of  smelting  nearly  one-half  on  heavy  sulphide  ore." 
This  I  take  to  mean  an  ore  consisting  principally  of  py- 
rite. This  effect  of  hot  blast  was  not  observed  either, 
but  note  that  3oc.  per  ton  of  ore  was  saved  by  doing 
away  with  it  altogether.  I  believe  that  hot  blast  shows 
to  the  best  advantage  on  these  ores,  or  rather  furnace 
charges,  which  are  short  in  heat-producing  iron  sul- 
phide. Each  worker  that  speaks  so  favorably  of  hot 
blast,  I  am  sure,  is  smelting  a  charge  which  contains 
more  than  20  per  cent  silica  and  less  than  30  per  cent 
iron  in  the  form  of  pyrite.  Variations  from  this  limit 
toward  more  silica  or  less  pyrite  call  for  more  heat,  and 
to  furnish  the  deficient  heat  a  relatively  small  increase 
in  coke  may  be  augmented  by  heating  the  blast. 

133 


PYRITE    SMELTING. 

The  observations  of  Dr.  Carpenter  on  the  utility  of 
hot  blast  are  in  parallel  with  my  own ;  but  I  do  not  hold 
with  him,  however,  as  to  the  entire  absence  of  lime  in 
the  slag.  I  have  usually  aimed  at  a  quarter  slag,  supply- 
ing lime  to  make  up  the  sum  of  the  earthy  bases  to  that 
ratio.  A  one-fifth  slag  will  work  well  and  clean,  but  re- 
ducing the  sum  of  the  bases,  other  than  iron,  below  that 
ratio  raises  the  iron  too  high  and  increases  the  specific 
gravity  of  the  slag.  Buttons  of  matte  commence  to 
show  in  the  bottoms  of  the  slag  pots.  In  fast  driving,  on 
pure  pyritic  ore,  excess  of  lime  will  also  prevent  a  good 
separation  of  matte  by  scattering  it  in  minute,  hollow 
beads  through  the  slag. 

The  smelting  practice  at  the  United  States  works  at 
Salt  Lake,  up  to  the  converting,  as  described  by  Mr. 
Read,  is  in  many  respects  similar  to  the  Mount  Lyell 
practice. 

Mr.  Godshall  and  Mr.  Weinberg  ask  for  more  infor- 
mation with  respect  to  the  elimination  of  hot  blast  at 
Mt.  Lyell.  I  doubt  if  very  exact  information  could  be 
obtained  for  the  reason  that  the  variations  in  the  prac- 
tice were  not  along  a  single  line  at  any  one  time.  At 
the  start  the  blast  was  heated  to  between  500°  and  600° 
F.,  with  the  pressure  varying  from  12  to  16  oz.  It  .was 
soon  observed  that  the  furnaces  drove  faster  under  in- 
creased blast,  and  when  the  No.  2  plant  was  built  pro- 
vision was  made  for  an  increased  quantity  of  blast  per 
furnace.  Starting  No.  2  plant  with  18  to  20  oz.  of  blast, 
the  pressure  was  gradually  increased  to  30  oz.  The 
blower  room  in  the  No.  I  plant,  being  most  disadvan- 
tageously  situated  on  account  of  the  growth  of  the  plant 
from  two  furnaces  to  six,  was  abandoned,  and  in  putting 
up  the  new  blower-room  the  same  size  blowers  were  put 
in  as  at  No.  2,  although  the  furnaces  of  the  No.  I  plant 
were  but  40  in.  by  168  in.,  as  against  the  42  in.  by  210 
in.  of  the  No.  2.  Greater  efficiency  in  the  furnace  work 
reduced  the  number  of  furnaces  run  in  the  No.  i  plant 

200 


G.  F.  BEARDSLEY. 

to  three  and  four,  so  that  within  certain  limits  there  was 
unlimited  blast  for  them.  The  cutting  down,  of  the  fuel 
in  the  hot-blast  stove  then  commenced,  and  as  the  fur- 
naces worked  colder  more  blast  was  put  on  until  the 
stoves  were  taken  off  entirely  and  the  blast  raised  to 
40  oz. 

In  addition  to  the  simultaneous  variation  of  blast  heat 
and  blast  pressure,  ores  purchased  from  outside  mines 
came  in,  and  the  use  of  pure  silica  was  more  or  less 
replaced  by  a  copper-bearing  aluminous  schist,  until  it 
finally  became  necessary  to  run  as  much  of  the  latter 
material  as  possible.  A  comparison  between  the  cost  of 
smelting  at  the  time  of  low-blast  pressure,  hot  blast, 
smaller  furnaces  and  reduced  tonnage,  as  against  the 
time  of  high  pressure,  cold  blast,  larger  furnaces  and 
increased  tonnage  can  be  made,  which  naturally  is  much 
in  favor  of  the  later  practice.  A  direct  comparison  be- 
tween hot  and  cold  blast,  on  a  plane  of  similarity  in  all 
other  conditions,  can  not  be  made  for  the  above  reasons. 
The  cost  of  the  hot  blast  under  the  earlier  conditions 
averaged  about  3oc.  and  under  the  later  condition  from 
2oc.  to  24c.  per  ton  of  ore. 

In  regard  to  the  loosely  held  atom  of  sulphur  in  FeS2 : 
considerable  effort  was  made  from  time  to  time  to  arrive 
at  the  proportion  of  sulphur  driven  off  before  actual 
fusion  of  the  pyrite  began.  Although  nothing  very  defi- 
nite was  arrived  at,  the  following  was  noted:  It  was 
usual  upon  shutting  down  a  furnace,  as  soon  as  the 
blast  was  off,  to  turn  a  hose  in  at  the  feed  doors,  cooling 
off  the  top  of  the  charge  and  allowing  the  men  to  get  in 
that  much  sooner  for  the  purpose  of  cleaning  out.  At 
times  the  shut-down  has  been  immediate ;  that  is,  with- 
out blowing  down,  due  to  failure  of  a  jacket,  cooling 
coil,  etc.,  and  consequent  flooding  of  the  lower  part  of 
the  furnace.  With  the  furnace  drenched  with  water,  top 
and  bottom,  an  action,  such  as  roasting,  etc.,  is  cut  short 
and  stopped.  Careful  examination  of  the  charge  under 

201 


PYRITE  SMELTING. 

such  circumstances  has  shown  no  recognizable  ore  be- 
low a  depth  of  2.5  ft.  from  the  surface  of  the  charge,  the 
charge  column  being  from  10  to  n  ft.  above  the  tuyeres. 
The  ore,  when  found,  had  the  composition  of  Fe,  55, 
and  S,  35.3,  which  closely  approximates  the  formula 
Fe8S9,  the  ordinary  constituents  of  the  ore  making  up 
the  balance.  The  heat  of  the  gases  coming  through  the 
charge  on  a  normal  furnace  was  several  times  deter- 
mined and  found  to  average  about  680°  F.  It  would 
seem,  therefore,  that  from  the  surface  of  the  charge  to 
three  feet  below  the  surface  of  the  charge  the  tempera- 
ture must  have  risen  from  680°  F.  to  the  melting  point 
of  pyrrhotite.  At  the  point  of  disappearance  of  the  pyr- 
rhotite,  the  slag,  which  was  the  next  easiest  constitu- 
ent of  the  charge  to  melt,  was  apparently  untouched, 
so  far  as  heat  was  concerned,  for  the  edges  of  the  pieces 
were  as  sharp  as  when  put  into  the  furnace. 

The  formation  of  the  pyrrhotite  and  its  sudden  dis- 
appearance to  a  great  extent  proves  the  absence  of  any 
considerable  quantity  of  free  oxygen  in  the  upper  part 
of  the  charge,  for  Valentine1  in  his  experiments  found 
that  FeS2  might  be  subjected  to  almost  any  degree  of 
heat  up  to  2,600°  F.,  in  the  absence  of  air,  and  retain  at 
least  30  per  cent  of  the  sulphur  out  of  the  53  per  cent 
present.  Another  curious  thing  noticed  was  that  pieces 
of  slag  from  low  down  in  the  furnace,  with  the  edges 
melted  off,  upon  breaking  after  cooling,  would  often 
show  more  or  less  pyrrhotite  in  very  thin  laminae  in  the 
checks  or  splits  in  the  center  of  the  piece. 

G.  F.  BEARDSLEY. 
San  Francisco,  June  5,  1904. 


in-ansactoms  American  Institute  Mining  Engineers,  Vol.  XVIII,  page  78. 
202 


CONTRIBUTION  BY  S.  DILLON-MILLS. 

The  Editor: 

Sir — Being  interested  to  some  small  extent  in  copper 
mining,  I  have  read  with  great  pleasure  some  of  the  dis- 
cussion on  pyrite  smelting,  and  recalling  some  of  my 
experience  of  bygone  years  in  blast-furnace  work,  it  has 
occurred  to  me  that  where  fuel  oil  can  be  obtained  at  a 
reasonable  cost  it  would  furnish  not  only  a  convenient 
means  of  experimenting  on  the  amount  of  extraneous 
fuel  required  with  different  varieties  of  ore,  but  also  a 
safeguard  against  chilling,  as  in  Mr.  Mathewson's 
work ;  the  supply  of  oil  can  be  adjusted  so  as  to  furnish 
either  a  reducing  or  an  oxidizing  flame,  and  any  irregu- 
larities in  the  working  of  the  furnace  can  be  met  as  soon 
as  perceived,  instead  of  having  to  await  the  working 
down  of  the  extra  fuel  with  the  stock  from  the  furnace 
top. 

I  recollect  on  one  occasion  having  five  out  of  the 
seven  tuyeres  of  a  charcoal  blast-furnace  closed  per- 
manently by  a  succession  of  slips  when  working  on  a 
very  dusty,  highly  aluminous,  brown  hematite  ore. 
Everything  looked  fair  for  a  regular  freeze-up,  as  we 
had  been  having  trouble  before  and  were  in  no  shape 
to  meet  this  additional  mishap.  I  had  some  oil  blow- 
pipes fixed  up  at  once,  and  in  36  hours  had  my  tuyeres 
all  bright  again,  and  the  iron  notch  in  good  shape,  it 
having  frozen  up  solid  This  was  done  with  about 
three-fourths  of  a  barrel  of  oil,  and  the  furnace  saved 
from  freezing  solid.  If  the  price  of  oil  permitted  doing 
so,  the  additional  fuel  required  might  be  altogether  sup- 
plied in  this  way,  as  the  oil  blow-pipe  can  be  easily  ad- 
justed to  form  a  permanent  attachment  to  the  tuyere, 

203 


PYRITE  SMELTING. 

without  interfering  with  the  line  of  sight  from  the  'peek- 
hole/  to  any  inconvenient  degree.  Of  course  in  the 
case  above  mentioned  the  tuyeres  had  to  be  removed, 
but  in  ordinary  cases  of  chilling  I  have  not  found  it 
necessary. 

S.  DILLON-MILLS. 
Toronto,  Canada,  July  6,  1904. 


204 


CONTRIBUTION  BY  L.  S.  AUSTIN. 

The  Editor : 

Sir — Dr.  Peters,  in  his  review  of  pyrite  smelting  in 
your  issue  of  July  21,  leaves  the  question  of  the  be- 
havior or  role  of  zinc  and  alumina  in  the  slag  unde- 
cided. In  so  doing  he  avoids  a  controversy  which  has 
prevailed  among  metallurgists  in  the  past,  and  espe- 
cially as  regards  the  action  of  alumina.  Many,  especially 
those  engaged  in  iron  smelting,  have  held  that  alumina 
is  to  be  regarded  as  an  acid  element  acting  much  in  the 
same  way  as  silica.  But  for  those  who  are  engaged  in 
pyrite  smelting,  where  lower  temperatures  and  irony 
slags  are  used,  the  conditions  are  very  different  from 
those  of  the  iron  blast  furnace.  The  conditions  of  the 
silver-lead  treatment  of  miscellaneous  ores  are,  in 
many  respects,  similar  to  those  prevailing  in  pyrite 
smelting,  with  the  difference  that  any  departure  from  a 
type  slag  in  silver-lead  smelting  is  accompanied  by  un- 
satisfactory working  and  metallurgical  losses.  Such 
slags  have,  therefore,  been  closely  studied.  Indeed, 
much  of  the  success  of  those  engaged  in  pyrite  smelting 
has  been  due  to  the  fact  that  men  engaged  in  it  have 
also  operated  silver-lead  blast  furnaces.  Indeed,  it  may 
be  personally  asserted  that  those  who  have  not  followed 
the  latter  practice  are  at  a  disadvantage  compared  with 
those  who  have,  because  they  have  not  been  compelled 
to  study  slag  composition  so  closely. 

The  behavior  of  zinc  and  alumina  in  a  slag  is  such  as 
to  obscure  the  mutual  action  of  its  acidic  and  basic  ele- 
ments, and  we  are  finding  to-day  a  portion  of  our  metal- 
lurgists adopting  a  very  different  way  of  looking  at 
these  relations,  which  has  resulted  in  their  using  a 

205 


PYRITE    SMELTING. 

working  hypothesis,  capable  at  least  of  satisfying  the 
varying  conditions  of  their  practice.  This  consists  in 
looking  upon  both  zinc  and  alumina,  not  as  bases,  but  as 
elements  singly  dissolved  in  the  molten  magma ;  that  is, 
they  are  non-effective  bases,  \vhich,  as  their  relative  pro- 
portion increases,  singly  stiffen  the  slag  much  as  sand 
stiffens  mortar.  Under  this  view  the  variables  to  be 
estimated  and  allowed  for  are,  for  the  acid  constituent, 
silica,  and  for  the  bases,  the  alkaline  earths,  iron  and 
manganese.  Under  this  hypothesis,  zinc,  whether  as 
sulphide  or  as  oxide,  stiffens  the  slag,  and  where  the 
quantity  of  slag  is  increased  by  the  use  of  a  larger 
proportion  of  silicious  ores,  the  slag  runs  smoother. 
This,  of  course,  is  the  same  as  diminishing  the  percent- 
age of  zinc  in  the  slag.  Alumina  is  to  be  regarded  as 
acting  in  the  same  way,  and  should  have  like  treatment. 
To  illustrate  the  manner  of  estimating  the  fluxes 
needed  in  making  a  slag  of  a  given  type,  we  will  take 
the  case  of  two  slags,  known  as  three-quarter  slags; 
that  is,  slags  in  which  the  ratio  of  lime  to  ferrous  oxide 
is  as  three  to  four.  We  have : 

1.  2. 

Si02 35.4  30.8 

FeO    (MnO)    31.8  27.7 

CaO  (MgO,  BaO)    24.7  21.5 

AlaOs,  ZnO,  ZnS,  K2O,  NaaO 8.1  200 

100.0  100.0 

In  the  first  instance  (i)  the  alumina  and  zinc  are  small 
relative  to  the  active  bases,  while  in  the  second  (2)  the 
percentage  is  large.  The  ratios  of  silica  to  the  active 
bases,  it  will  be  observed,  lemain  the  same.  In  the 
second  case  (2)  the  zinc  and  alumina  become  too  much 
to  be  capable  of  being  dissolved  in  so  small  an  amount 
of  accompanying  silicates,  and  hence  the  reason  why  I 
have,  in  a  former  article  on  pyrite  smelting,  limited  the 
zinc  to  10  per  cent  of  the  slag  for  easy  running.  How- 
ever, while  the  proportions  given  are  ideal  for  obtain- 
ing lead-free  slags,  when  it  comes  to  the  question  of 

200 


L.  S.  AUSTIN. 

fusibility  only,  the  ferrous  iron  may  be  advantageously 
increased  and  the  lime  decreased  from  the  proportions 
just  given.  What  I  wish  particularly  to  bring  out  is 
that,  in  our  working  hypothesis,  neither  zinc  nor  alu- 
mina is  to  be  reckoned  as  an  active  base,  nor  is  the 
latter  as  acidic  in  its  action.  When  an  aluminous  slag 
has  a  so-called  acid  appearance,  it  is  due,  not  to  the 
alumina  acting  as  an  acid,  but  because  it  is  a  solute 
which  has  made  the  molten  mass  more  viscous. 

The  preceding  observations  apply  to  type  slags 
which  do  not  exceed  36  per  cent  silica.  When  we  come 
to  the  acid  slags,  other  conditions  prevail.  Since  any 
given  element  in  a  slag  seeks  to  combine  with  other  ele- 
ments in  proportion  to  its  needs,  it  follows  that  the 
large  proportion  of  silica  present  is  eager  to  regard  alu- 
mina as  a  base,  and  it  no  doubt  does  so.  How,  other- 
wise, can  we  account  for  the  fusibility  of  the  viscous 
high-silica  slags,  sometimes  reaching  65  per  cent  silica  ? 
Such  slags  have  a  corrosive  effect  upon  basic  or  even  on 
neutral  linings,  and  where  lead  is  present  are  cleaned 
from  it  with  great  difficulty. 

L.  S.  AUSTIN. 
Houghton,  Mich.,  Aug.  8,  1904. 


207 


CONTRIBUTION  BY  HERBERT  LANG. 

The  Editor: 

Sir-— Properly  conceived  answers  to  the  ten  ques- 
tions on  pyrite  smelting  which  have  been  propounded, 
would  seem  to  cover  the  purely  practical  features  of  the 
art  very  satisfactorily,  but  their  bearing  is  too  severely 
practical  to  admit  of  as  broad  a  treatment  as  the  sub- 
ject in  general  demands,  or,  perhaps  I  should  say,  as  the 
requirements  of  the  metallurgical  student  make  neces- 
sary. May  I  suggest,  then,  in  view  of  the  probable  per- 
petuation of  the  replies  in  book  form,  that  an  exten- 
sion of  the  topic  along  more  theoretical  and  general 
lines  would  be  welcome  to  the  beginners  in  smelting, 
to  whom,  I  suppose,  all  such  publications  are  ultimately 
addressed?  At  the  risk  of  trenching  upon  your  valu- 
able space  I  will  take  the  liberty  of  propounding  two 
more  questions,  in  my  opinion  of  a  nature  to  bring  out 
the  general  relations  of  the  pyritic  to  the  ordinary  mat- 
ting process,  and  will  provide  these  with  the  very  brief- 
est of  answers,  more  in  the  hope  of  evolving  the  opinions 
of  others  than  in  the  expectation  of  adding  a  lasting  and 
important  part  to  the  completed  treatise. 

The  questions  that  I  would  ask  and  answer  are 
these : 

What  are  the  differences  in  principle  between  the  pyritic 
and  the  ordinary  matting  process? 

What  are  the  differences  in  practice  ? 

Question  I. — Before  attempting  to  consider  the  dif- 
ferences in  theory  between  the  two  processes,  it  will  be 
useful  to  briefly  review  the  state  of  opinion  regarding 
the  principal  chemical  reactions  which  occur  in  the  ordi- 
nary form  of  matting.  In  this  connection  it  is  the  cus- 

208 


HERBERT  LANG. 

torn  to  group  the  phenomena  in  three  classes ;  the  first 
including  those  reactions  that  furnish  heat,  the  second 
those  to  which  slag  formation  is  due,  and  the  third  those 
concerned  in  the  production  of  matte.  Of  the  first  class, 
the  only  one  which  concerns  the  present  inquiry  is  the 
leaction  between  the  oxygen  of  the  blast  and  the  car- 
bonaceous fuels.  The  imported  products  of  this  reaction 
are  carbon  monoxide  and  carbon  dioxide,  both  of  which, 
being  gaseous,  tend  to  escape  into  the  atmosphere. 
Incident  to  this  reaction  is  the  reduction  of  certain 
iron  and  manganese  compounds  from  the  condition 
of  peroxide  to  that  of  protoxide,  and  of  lime  from 
that  of  carbonate  to  the  caustic  form,  fitted  to 
combine  with  the  silica  present  and  to  carry  out  the 
reactions  of  the  second  class.  The  latter  consist  in  the 
combination  of  the  thus  prepared  and  other  bases  with 
the  free  silica,  or  the  re-formation  of  previously  exist- 
ing silicates — all  these  products  becoming  dissolved  into 
slag.  Attendant  phenomena,  as  the  reduction  to  the 
metallic  state  of  small  quantities  of  iron,  and  the  pro- 
duction of  heat  through  the  silicatization  of  oxides,  may 
be  disregarded  in  this  connection.  The  third  group 
of  reactions  is  more  obscure,  but  their  net  result  is  the 
production  of  matte  by  the  agency  of  sulphur,  which 
attacks  with  varying  degrees  of  energy  the  metals  ex- 
posed to  its  influence,  allying  itself  preferentially  with 
the  copper,  the  silver  and  the  nickel,  and  secondarily 
with  iron,  lead,  etc.,  and  forming  fusible  and  compara- 
tively stable  compounds  with  all  of  them.  This  bald 
statement  of  accepted  fact  must  serve  as  a  basis  of  com- 
parison between  the  two  processes. 

In  pyrite  smelting  the  fuel,  instead  of  coke,  is  sub- 
stantially the  sulphide  of  iron.  It  may  be  matte  which, 
for  the  second  time,  is  passing  through  the  smelting 
furnace ;  it  may  be  pyrrhotite  ;  or  it  may  be  pyrite  which, 
in  descending  to  that  part  of  the  furnace  where  its  fuel 

209 


PYRITE  SMELTING. 

properties  become  available,  has  parted  with  a  portion 
of  its  sulphur.  No  other  sulphide  which  possesses  the 
requisite  properties  is  found  in  sufficient  quantity  to 
make  it  available  in  the  process.  The  reactions  pro- 
duced between  the  molten  sulphide  and  the  air  blast  are 
comparable  in  their  heat-making  powers  with  those  be- 
tween carbon  and  the  air;  but  here  the  comparison 
ceases.  In  pyrite  smelting  the  three  classes  of  reactions 
previously  cited,  namely,  the  heat-making,  slag-making 
and  matte-making,  are  concurrent  and  coincident  to  a 
remarkable  degree,  which  furnishes  the  first  point  of 
theoretical  difference  between  the  processes.  Thus,  the 
heat-producing  reaction  between  the  metallic  base  of 
the  sulphides  and  the  oxygen  of  the  blast  has,  as  a 
secondary  and  simultaneous  effect,  the  production  of  ox- 
ides for  the  formation  of  slags,  and  it  is  this  detail  of 
the  reaction  which  constitutes  the  indispensable  charac- 
teristic of  the  operation  and  differentiates  it  from  all 
other  smelting  processes.  In  a  previous  writing,  I 
took  occasion  to  point  this  out  as  the  chief  characteristic 
of  the  method,  and  to  deduce  from  it  the  definition  of 
the  process  as  follows: 

Pyrite  smelting  is  that  department  of  blast-furnace 
smelting  in  which  metallic  oxides  are  formed  in  the  fur- 
nace. 

This  effect,  while  not  absolutely  peculiar  to  the  pyritic 
method,  yet  furnishes  its  chief  characteristic.1  B^  this 
one  reaction  (or  rather  by  the  group  of  reactions 
which  we  are  in  the  habit  of  typifying  by  this  one)  the 
heat  necessary  for  the  work  is  generated,  and  the  prin- 
cipal slag-making  bases  necessary  for  absorbing  the 
silica  present  are  produced.  Notice  the  peculiar  reci- 
procal relations  of  the  matte-making,  heat-making  and 
slag-making  forces.  With  a  given  charge,  the  heat  set 
free  and  the  amount  of  oxides  formed  are  in  inverse 

iThe  unimportant  formation  of  ZnO  from  ZnS  in  the  lead  furnace  has  been 
instanced  as  affecting  the  theoretical  accuracy  of  this  definition. 

210 


HERBERT  LANG. 

ratio  to  the  amount  of  matte  made.  The  greater  the 
quantity  of  sulphides  decomposed,  the  greater  the 
quantity  of  heat  generated,  the  greater  the  amount  of 
iron  driven  into  the  slag,  and  the  less  the  amount  of 
iron  remaining  to  swell  the  matte-fall.  This  feature  of 
the  process  is  very  remarkable  indeed,  and  is  worthy  of 
much  consideration  by  the  student.  He  should  not  fail 
to  bear  in  mind  that  it  is  the  iron  which  really  does  the 
work,  and  that  without  it  we  could  have  only  the  faint- 
est approximation  to  pyrite  smelting.  It  is  idle  to  speak 
of  zinc  as  being  in  any  sense  a  useful  substitute  for  iron 
in  pyritic  work.  Iron  is  the  key  of  the  process  and  al- 
ways will  remain  so. 

The  simplest  practicable  charge  for  the  pyritic  blast 
furnace  consists  of  iron  sulphide  mixed  with  quartz. 
The  ready  fusibility  of  the  former,  coupled  with  the  in- 
fusibility  of  the  latter,  bring  about  some  significant  con- 
ditions which  are  receiving  much  attention  of  late.    The 
sulphide  melts  at  a  very  moderate  temperature,  say,  of 
about  i, 000°  C,  at  which  the  quartz  is  not  in  the  least 
affected.     When  thrown  together  into  the  furnace,  the 
sulphide  melts  before  it  has  got  down  far,  and  the  liquid 
tends  to  descend  into  the  hearth,  while  the  quartz  sinks 
by  itself  in  a  mass  downward  to  the  tuyeres.     The  fluid 
sulphide,  getting  hotter  as  it  descends  through  the  inter- 
stices of  the  quartz  mass,  meets  the  upward  current  of 
air  from  the  tuyeres,  while  both,  as  well  as  the  quartz, 
are  at  their  hottest,  and  in  condition  to  be  most  quickly 
acted  upon.     The  reaction  that  ensues  results  in  cutting 
away  the  quartz  mass,  which  is  as  rapidly  supplied  by 
fresh  fragments  from  above.     Slag  is  thus  produced, 
while  the  residue  of  the  melted  sulphide  forms  matte, 
and  both  gather  in  the  hearth.     No  doubt  the  effective 
heating  of  the  blast,  so  often  alluded  to  by  contem- 
porary writers,  is  done  by  contact  with  the  descending 
fluids  rather  than  by  the  hardened  masses  of  partially 
cooled  slag  which  attach  themselves  about  the  tuyeres, 

211 


PYRITE    SMELTING. 

forming  noses.  It  is  very  evident  that  if  a  mass  of 
slag  stops  on  the  road  down  its  usefulness  as  a  heating 
medium  must  soon  be  lost,  for  the  heat  contained  in  it 
would  be  as  nothing  compared  with  that  necessary  to 
elevate  noticeably  the  temperature  of  the  blast.  It  is 
the  sinking  mass  which  heats  the  blast.  We  may  recog- 
nize virtually  two  working  zones,  the  one  being  that 
where  the  sulphides  are  melted,  the  other  that  where 
the  infusible  materials  await  the  action  of  the  fused 
sulphides.  This  statement,  which  recognizes  the  per- 
petual existence  of  what  I  have  called  the  quartz  mass, 
better  characterizes  the  condition  of  things  than  that 
wherein  the  delayed  mass  is  spoken  of  as  accretionary 
and  accidental — a  view  got  by  inspecting  the  furnace's 
interior  through  the  tuyeres. 

When  more  complex  charges  are  fed,  containing 
limestone,  natural  silicates,  slag,  and  perhaps  other 
materials,  more  complicated  reactions  will  ensue,  and 
somewhat  different  results  will  be  got.  The  quartzose 
mass  will  still  exist  in  form,  but  its  composition  will  have 
changed.  It  will  still  be  infusible  by  itself,  since  it  is  not 
conceivable  that  the  pyritic  process  could  go  on  without 
the  aid  of  the  iron  oxide  in  the  formation  of  slag.  We 
may  believe  that  the  quartzose  materials  are  cut  away 
by  the  descending  matte  stream,  something  in  the  man- 
ner that  ice  is  cut  away  by  a  stream  of  hot  water.  It 
being  the  freshly  formed  oxide  that  unites  with  the 
silicious  matters,  it  is  evident  that  the  quartz  must 
remain  until  enough  oxide  is  formed  to  destroy  it.  If 
there  is  more  matte  than  necessary  for  uniting  with  the 
silica,  it  brings  up  in  the  hearth,  carrying  in  combina- 
tion with  it  the  gold,  silver  and  copper  of  the  charge. 

If  we  may  judge  by  what  they  have  written,  it  is  the 
general  impression  among  metallurgists  that  the  con- 
trolling reaction  of  the  pyritic  furnace  should  be  repre- 
sented thus: 

(A)         FeS  +  30  =  FeO  +  SO2. 

212 


HERBERT  LANG. 

And  that  this  is  succeeded  by  another  reaction,  in  which 
the  ferrous  oxide  is  scorified  and  added  to  the  slag  as 
silicate.  Uncombined  oxygen  must,  according  to  this 
view,  exist  in  the  lower  part  of  the  furnace,  else  there 
would  be  no  decomposition  of  the  sulphide.  Also  the  de- 
composition, with  concurrent  production  of  heat,  would 
be  in  proportion  to  the  amount  of  air  present.  Then  the 
quantity  of  air  present  would  inevitably  govern  the 
smelting,  without  regard  to  the  incombustible  con- 
stituents of  the  charge.  According  to  this  view,  it 
would  be  necessary  to  have  at  all  times  a  certain  amount 
of  free  oxygen  in  the  furnace,  else  the  work  would 
cease,  and  neither  heat,  slag  nor  matte  would  be  pro- 
duced. Some  considerations  affecting  these  results 
make  it  seem  improbable  that  this  can  be  precisely  the 
way  in  which  the  effects  are  brought  about.  Let  us 
suppose  a  furnace  working  on  the  pyritic  plan,  wholly 
without  carbonaceous  fuel.  Next  let  us  suppose  that 
a  portion  of  coke  be  added  to  the  charge  but  which  re- 
mains otherwise  as  before.  The  coke  having  a  greater 
affinity  for  the  oxygen  than  any  other  substance  pres- 
ent, the  effect  will  be  to  diminish  the  quantity  of  the 
oxygen  available  for  decomposing  the  sulphides,  and,  as 
a  consequence,  there  will  be  less  oxide  of  iron  set  free 
to  slag  the  silica.  The  matte,  being  swelled  by  the 
addition  of  the  unaltered  sulphides,  will  fall  more  copi- 
ously. The  effect  of  the  increased  acidity  of  the  slag 
will  be  to  cause  the  furnace  to  run  slower,  and  perhaps 
to  close  up  entirely  from  the  formation  of  incrustations 
about  the  smelting  zone.  But  such  is  not  the  experi- 
ence. We  may  add  5,  10  or  even  15  per  cent  of  coke 
to  such  a  charge  without  inducing  any  such  effects,  or 
even  without  any  injurious  effects  at  all.  When  the 
coke  exists  in  so  large  a  proportion,  it  is  difficult  to  see 
how  the  atmosphere  in  the  shaft  can  remain  in  a  con- 
dition to  bring  about  the  real  pyritic  effects  if  they 
depend  so  entirely  upon  the  presence  of  free  oxy- 

213 


PYRITE  SMELTING. 

gen,  and  especially  if  we  remember  that  much  satis- 
factory pyritic  work  has  been  done  with  as  high  a  coke 
charge  as  12  and  even  15  per  cent.  These  high 
coke  percentages,  which  to  the  everyday  view  would 
seem  to  forbid  pyritic  work  entirely,  really  allow 
uncommonly  extensive  decomposition  of  the  sulphides, 
evidenced  by  a  high-grade  matte  product,  while  the 
work  goes  on  swiftly  and  regularly.  Much  evidence 
might  be  cited  to  prove  that  the  strongly  oxidizing 
powers  inhabiting  the  interior  of  the  pyritic  furnace  are 
not  so  closely  contingent  upon  the  assumed  presence  of 
free  oxygen  as  has  been  assumed.  In  such  cases  we  have 
not  only  the  presumptive  evidence  of  the  coke  charged, 
but  that  of  the  evolved  gases,  which  often  have  been  ob- 
served to  contain  free  elemental  sulphur,  sulphide  of  ar- 
senic, etc.,  which  could  not  exist  in  the  presence  of  free 
oxygen  in  the  heated  furnace  for  a  moment.  What 
lessons  do  we  draw  from  these  suggestive  facts? 

In  the  first  place,  may  wre  not  question  the  accuracy 
of  the  notion  that  free  oxygen  is  the  governing  factor 
in  the  case  ?  May  it  not  be  that  silica  rather  than  oxy- 
gen is  the  controlling  factor?  My  view  of  what  takes 
place  in  the  carbonless  charge  I  have  embodied  in  the 
following  equation,  which  seems  to  me  to  conform  more 
closely  than  the  other  to  what  is  known  to  occur : 

(B)  2FeS  +  SiO2  +  2O  =  (FeO)2  SiO2  +  S^, 
This  equation  indicates  the  simultaneous  decomposition 
of  the  sulphide,  the  slagging  of  the  produced  oxide  of 
iron,  and  the  expulsion  of  the  sulphur.  The  latter  will 
burn  if  there  be  free  oxygen  to  combine  with  it,  but  if 
not  it  will  issue  from  the  stack  in  the  elemental  form. 
Usually  it  passes  off  as  a  mixture  of  sulphur  with  sulphur 
dioxide.  When  it  exists  in  the  stock  in  large  proportions 
it  is  impossible  to  burn  all  to  dioxide.  In  the  converter 
process  the  case  is  the  same,  part  of  the  sulphur 
escaping  as  dioxide,  part  as  elemental.  In  both  pro- 
cesses the  iron  is  found  to  be  far  more  avid  for  oxygen 

214 


HERBERT  LANG. 

than  the  sulphur,  whence  the  latter  is  kept  from  com- 
bination when  there  is  not  enough  oxygen  for  both  the 
elements.  From  a  heat-producing  point  of  view  sul- 
phur is  not  of  great  importance  in  either  process,  al- 
though the  impression  is  very  common  that  pyrite 
.smelting  owes  its  existence  to  the  heat-giving  effects 
of  the  sulphur.  I  presume  that  if  we  were  to  examine 
closely  into  the  rationale  of  such  a  process  as  heap- 
roasting,  for  instance,  we  should  find  that  to  the  oxida- 
tion of  the  iron  and  not  to  that  of  the  sulphur  were 
due  its  principal  effects,  and  that  the  latter  played  very, 
little  part  in  the  work. 

The  familiar  assumption  that  the  pyritic  effects  are 
only  possible  in  the  presence  of  a  large  proportion  of 
free  oxygen,  seems  to  be  shaken  by  the  foregoing 
consideration,  and  it  even  may  be  rationally  asked 
if  any  free  oxygen  at  all  is  necessary  to  the  pro- 
cess. Evidently  oxygen  must  be  had  from  somewhere, 
and  if  we  imagine  conditions  wherein  all  that  contained 
in  the  air  would  be  taken  up  and  wherein  none  in  an 
available  state  is  brought  in  by  components  of  the 
charge,  it  would  still  be  an  unsettled  question  whether 
the  process  could  go  on  or  not.  That  it  can  go  on  in 
the  presence  of  15  per  cent  of  coke  is  the  most  remark- 
able peculiarity  of  the  process  yet  made  out.  The 
probable  effects  in  eliminating  the  oxygen  at  a  short 
distance  from  the  tuyeres  naturally  lead  to  the  impor- 
tant question  if  the  oxygen  necessary  may  not  be  de- 
rived in  such  cases  from  the  carbon  dioxide  previously 
formed  by  the  action  of  the  blast  upon  the  fuel.  This 
is  not  an  unlikely  supposition  by  any  means,  as  anal^ 
ogous  reactions  are  not  uncommon.  Further  research 
is  necessary,  however,  to  settle  the  subject  conclusively.; 
If  we  assume  that  the  dioxide  has  such  an  action,  it 
would  put  the  process  on  a  very  different  plane  from 
that  it  now  occupies,  but  would  still  leave  us  in  the  dark 

215 


PYRITE    SMELTING. 

as  to  the  extent  to  which  the  addition  of  coke  could  be 
carried.  It  is  quite  evident  that  ultimately  a  point 
must  be  reached  at  which  a  further  addition  would  be 
fatal  to  the  process,  as  taking  up  all  the  available  oxy- 
gen with  the  formation  only  of  monoxide,  which  can 
hardly  be  expected  to  have  any  action  on  the  sulphides, 
although  it  is  known  to  have  effect  upon  certain  metals 
of  the  iron  group.  The  chemical  formula  which  repre- 
sents the  interaction  of  iron  sulphide  upon  silica  and 
carbon  dioxide  is : 

(C)  2FeS  +  SiO2+  2CO2  =  ( FeO) 2,  SiO2+  2CO  +  S2. 
My  views  as  to  the  functions  of  silica  in  the  pyritic 
furnace  were  first  published  in  The  Engineering  and 
Mining  Journal  as  early  as  1897.  I  positively  assert  the 
validity  of  reaction  (B)  as  the  real  controlling  and 
characteristic  reaction  of  the  pyritic  furnace,  although 
not  by  any  means  the  only  one  that  occurs  or  may  occur 
therein. 

Equation  (A)  I  am  in  the  habit  of  calling  the  iron- 
sulphur-oxygen  reaction,  while  (B)  in  my  terminology  is 
the  iron-silica  reaction.  In  both  I  assume  that  the  sin- 
gulo-silicate  of  iron  is  formed,  which  I  believe  to  take 
place  invariably  in  this  form  of  smelting. 

The  differences  between  the  slag — and  especially  the 
matte-forming  activities  of  the  two  processes — are 
exemplified  by  the  behavior  of  the  inferior  elements, 
arsenic,  antimony,  bismuth  and  lead,  whose  expulsion 
from  the  pyritic  charge  affords  an  unequaled  means  of 
purifying  the  furnace  products.  A  discussion  of  these 
effects,  or  even  a  further  reference  to  the  general  ques- 
tion of  slag-  and  matte-formation,  would  occupy  too 
much  space  for  the  present,  and  I  will  pass  on  to  Ques- 
tion 2 — Differences  in  practice  between  pyritic  end  ordinary 
matting. 

Neither  furnaces  nor  accessory  apparatus  have  been 
much  modified  as  yet  by  considerations  of  theory. 

216 


HERBERT  LANG. 

In  the  early  days  of  pyrite  smelting,  when  light 
blast  and  slow  driving  were  the  rule,  furnaces  with 
straight  sides  had  their  advocates,  myself  among  them. 
Their  virtue,  probably  a  real  one,  has  been  obscured  by 
the  faster  and  harder  rate  of  driving  now  in  vogue.  The 
universal  tendency  has  been  to  reproduce  the  familiar 
forms  of  the  lead-  and  copper-smelting  furnaces  and 
adjuncts,  without  regard  to  possible  improvements 
other  than  increased  size  and  blowing  power.  Blast 
pressures  have  been  increased  quite  up  to  the  limit  of 
the  ordinary  rotary  blowers,  and  the  tendency  being 
toward  still  higher  pressures,  it  seems  as  if  piston 
blowers  are  likely  to  become  fashionable  in  this  pursuit, 
especially  as  it  is  declared  by  some  practitioners  that  a 
high-pressure  cold  blast  can  be  made  to  serve  the  same 
purpose  as  a  warm  or  hot  one  of  lower  pressure.  The 
choice  evidently  is  to  be  determined  by  which  is  the 
cheaper,  the  cold,  hard  blast  or  the  warm,  or  hot,  light 
blast.  If  I  interpret  the  progress  and  the  tendencies 
of  the  age  aright,  the  time  is  not  far  away  when 
pyrite  smelters  will  be  borrowing  the  furnaces  and 
apparatus  of  the  pig-iron  makers.  In  fact,  I  have 
for  some  time  believed  that  we  could  not  do  better 
than  put  up  works  in  precisely  the  style  of  the 
great  iron  blast-furnace  plants  of  the  East  to  do 
pyritic  work  in.  The  furnaces  doubtless  would  have 
to  be  cut  down  somewhat,  but  aside  from  this  I 
can  see  no  alteration  that  good  sense  could  dictate. 
The  blowing  engines,  the  firebrick  hot-blast  stoves,  the 
charging  apparatus,  the  slag-  and  metal-conveying  ma- 
chinery— all  these  are  so  much  more  effective  than  the 
comparatively  trivial  and  labor-wasting  tools  of  the  cop- 
per smelter  that  there  is  no  comparison. 

HERBERT  LANG. 
Oakland,  Cal.,  August  8,  1904. 

217 


CONTRIBUTION  BY  WALTER  E.  KOCH. 

The  Editor : 

Sir — The  following  additional  notes  may  be  of  ser- 
vice :  We  find  slags  below  5  per  cent  in  lime  chill  quickly, 
and  that  slags  above  10  per  cent  in  lime  do  not  sepa- 
rate out  the  values  so  well  as  when  kept  below  10  per 
cent  lime.  A  7  to  8  per  cent  lime  slag  is  ideal.  On 
cleaning  flues  we  found  the  cold  blast  made  more  than 
double  the  quantity  of  flue-dust  made  by  the  hot  blast, 
and,  worse  still,  the  cold-blast  flue-dust  from  the  same 
ores  contained  double  the  value  of  the  hot-blast  flue- 
dust.  Altogether,  as  compared  with  hot  blast,  the  cold- 
blast  runs  were  miserable  and  expensive  failures.  In 
July  we  had  another  freeze-up  on  cold  blast.  The  July 
run  showed  a  trifle  better  in  coke  consumption  (10.5  in- 
stead of  ii  per  cent),  but  the  ore  charged  was  only  30 
tons  per  24  hours  and  the  matte  outfall  was  unsatis- 
factory. However,  with  July  our  cold-blast  runs  came 
to  an  end — for  which  we  are  truly  thankful.  This 
month  we  hope  to  run  with  hot  blast,  gas-engines  and 
modern  appliances  and  leave  behind  us  the  Paleozoic 
period  of  cold  blast  and  steam-engines.  With  hot  blast, 
gas-engines  and  electric  transmission,  the  twentieth 
century  smelter  has  a  brilliant  and  economical  future. 

WALTER  E.  KOCH. 
Santa  Maria  del  Oro,  Sept.  2,  1904. 


218 


CONTRIBUTION  BY  G.  F.  BEARDSLEY. 

The  Editor : 

Sir — Before  the  collected  articles  on  pyrite  smelting 
appear  in  book  form  I  would  like  to  add  a  few  words 
on  the  effect  of  alumina  in  the  pyrite  furnace. 

It  has  been  noted  that  the  furnace,  in  this  process, 
seems  to  select  its  own  slag.  This  is  quite  true,  and  an 
apparent  reason  is  at  first  offered  by  the  fact  that  the 
iron  oxidized  by  the  furnace  is  a  factor  in  the  formation 
of  the  slag  over  which  the  metallurgist  has  but  little 
control.  The  quantity  of  lime  may  be  varied  in  the 
slag  within  certain  limits,  so  also  any  other  constituent 
added,  but  not  so  the  iron.  Small  causes  will  vary  the 
rate  of  oxidation  in  the  furnace,  and  consequently  the 
amount  of  iron  oxide  supplied  to  the  slag,  but  this 
variation  does  not  affect  it  materially.  The  relation  of 
silica  to  iron  remains  about  the  same. 

The  true  reason  of  the  pyrite  furnace  apparently  se- 
lecting its  own  slag  will  be  found  in  the  fact  that  the 
slag  is  emitted  from  the  furnace  at  the  lowest  formation 
temperature  possible  with  the  slag-forming  material 
supplied.  Matte  and  slag  that  are  free  to  move  from  a 
source  of  heat  will  commence  to  flow  at  a  temperature 
not  far  above  that  of  their  formation.  If  the  flow  is 
hindered  by  their  having  to  make  their  way  or  part  of 
their  way  through  a  mass  of  incandescent  material,  or 
by  having  to  move  by  a  tortuous  passage  to  an  exit,  they 
will  continue  to  absorb  heat  only  until  the  heat  im- 
parted to  them  is  balanced  by  the  heat  removed  by  the 
rapidity  of  the  flow. 

The  oxygen  ratios  in  the  slags  formed  by  this 
method  of  working  vary  from  the  singulo-silicate,  in 

219 


PYRITE  SMELTING. 

which  the  ratio  of  the  oxygen  of  the  acid  to  the  oxygen 
of  the  base  is  as  I  to  i,  to  those  slags  in  which  the  ratio 
is  as  8  to  5.  The  majority  of  slags  fall  within  the  4  to 
3  ratio.  The  following  block  out  of  Prof.  Richards' 
slag  table,  as  published  by  Hofman,1  covers  the  whole 
range  of  pyrite  slags,  as  far  as  I  am  aware,  my  obser- 
vations extending  over  some  1,800  slag  analyses  made 
in  three  different  works. 


Formulae  of 
Silicates. 

2  BO  SiOf 

O  in  bases 
to 
O  in  acid. 
(FeO 
2  :2  <  CaO 

65.60 
8 
86.40 
62.66 
8 
39.34 

Percentages. 
57.58           53.24 
12                 16 
80.42           30.76 
63.58           49.24 
12                 16 
34.42           34.76 
51.20           46.70 
12                 16 
36.80           37.30 
48.22           43.78 
12                 16 
39.78           40.22 
46.62           42.17 
22                  16 
41.37           41.83 

48.90 
20 
31.07 
44.93 
20 
35.07 
42.25 
20 
37.75 
39.34 
20 
40.66 
37.72 
20 
42.28 

5BO  3SiOj 

,(  SiO, 
(FeO 
5  '3X2  <  CaO 

8BO  2SiO2 

(SiOj 
(FeO 
3  -2X2  <  CaO 

4BO  3SiOj 

(Si02 
(FeO 
4  '3X2  \  CaO 

6BO  4SiOj 

(SiOa 
(  FeO 
4  -4X2  \  CaO 

(Si02 

If  these  are  traced  through  his  tables  of  formation 
temperatures  they  will  all  be  found  to  be  among  the 
lowest  temperatures  determined. 

With  a  pure  pyrite  or  pyrrhotite  ore,  to  which,  if  not 
already  present,  silica  is  added,  there  will  result,  after 
an  oxidizing  smelting,  a  simple  silicate  of  iron  of  low 
formation  temperature  and  low  melting  point.  Lime 
added  to  this  in  proper  proportion  invariably  lowers  the 
formation  temperature,  and  some  of  the  lime  may  be 
replaced  by  alumina  without  materially  affecting  the 
slag  in  this  respect.  The  general  tendency  of  alumina, 
however,  is  to  raise  the  melting  point  of  slags  and  to  in- 
crease their  viscosity,  the  latter  being  a  very  undesir- 
able quality,  as  it  interferes  with  the  proper  settlement 
of  the  matte. 

1  'Temperature  at  which  Certain  Ferrous  Silicates  and  Calcic  Silicates 
are  Formed  in  Fusion,'  etc.  Transactions  American  Institute  Mining 
Engineers,  Vol.  XXIX,  page  682. 

220 


G.  F.  BEARDSLEY. 

It  is  seldom  that  uncombined  alumina  forms  a  part 
of  the  smelting  charge,  for  the  reason  that  pyrite  ores 
are  usually  associated  with  schist,  porphyry,  etc.,  and 
often  the  ore  itself  contains  aluminous  minerals,  as  is 
the  case  with  the  Tennessee  pyrrhotite.  If  there  is 
added  to  the  smelting  charge  a  natural  silicate  of  alu- 
mina of  the  bi-  or  tri-  or  high  r  silicate  order,  there 
will  be  no  breaking  up  of  this  combination,  as  the  heat 
of  the  low  temperature  slags  is  not  sufficient  to  effect  it. 
There  will  be  dissolved  just  so  much  of  this  aluminous 
silicate  as  the  slag  can  carry  at  the  given  temperature, 
and  no  more.  If  there  is  more  of  this  silicate  than  the 
slag  can  dissolve,  it  is  left  behind  in  the  lower  part  of 
the  furnace,  and  the  fusion  zone  is  forced  higher  and 
higher  until  the  charge  finally  smelts  on  top  and  the 
furnace  suddenly  freezes  up. 

In  furnaces  running  on  a  reduction  smelting,  with  9 
to  15  per  cent  of  coke  on  the  charge,  slags  from  the 
fusion  zone  above  the  tuyeres  continue  to  absorb  heat 
or  become  superheated  by  running  through  the  incan- 
descent fuel  below,  and,  as  their  heat  rises,  they  become 
more  and  more  capable  of  breaking  up  or  absorbing 
combinations  having  a  higher  melting-point. 

It  seems  to  me  that  the  slags  first  formed  in  any 
blast-furnace  work  must  be  of  the  simplest,  low-tem- 
perature formation,  silicate  order  that  can  be  made 
from  the  constituents  present  at  that  point,  and  as  the 
superheating  goes  on,  silicates  of  a  higher  formation 
temperature  are  merely  dissolved  in  it  with  a  probable 
decomposition  after  solution. 

The  working  limit  of  alumina  in  pyrite  slag  made 
direct  from  ore  is  about  7  per  cent,  and  although  this 
may  be  forced  to  8  per  cent  or  9  per  cent  for  a  time, 
trouble  is  pretty  sure  to  result.  A  furnace  concentrat- 
ing low-grade  matte,  from  the  first  operation  to  a  40 
per  cent  or  50  per  cent  converter  matte,  runs  very  much 

221 


PYRITE    SMELTING. 

hotter  than  an  ore  furnace,  and  under  these  conditions 
it  should  be  possible  to  add  to  the  slag  a  full  10  per  cent 
of  alumina  through  the  fluxes,  if  required. 

To  illustrate  the  effect  of  an  excess  of  an  aluminous 
material  in  pyrite  work,  the  following  is  cited:  At  a 
plant  which  had  been  heap-roasting  their  output  for  a 
number  of  years  an  ordinary  orthoclase  quartz-porphyry 
was  used  as  a  flux  for  the  roasted  material,  and  the 
furnace  ran  very  well.  The  analyses  of  the  green  ore 
(unroasted  pyrite)  and  the  porphyry  were  as  follows : 

Green  Ore.    Porphyry. 

Silica 5  77.30 

Iron   35  2.75 

Alumina Trace.  15.20 

Lime Nil.  0.63" 

Zinc   6                    

Sulphur 43  \           .... 

Copper 6  .... 

With  the  exception  of  possible  trouble  with  the  zinc, 
the  ore  seemed  eminently  suitable  for  pyrite  treatment, 
and  this  was  resolved  upon.  As  quartz  was  a  some- 
what expensive  flux  and  the  porphyry  exceedingly 
cheap,  an  endeavor  was  made  to  retain  the  latter, 
though  it  was  soon  found  to  be  conducive  of  bad  work. 
Later  an  experimental  run  was  made,  with  the  following 
results :  The  furnace  was  blown  in  as  usual  at  9  a.  m., 
and  run  on  a  quartz  flux  until  12 150  p.  m.,  to  make  all 
furnace  conditions  as  perfect  as  possible;  at  that  hour 
no  other  alteration  was  made  in  the  charge  except  to 
change  quartz  for  porphyry.  At  4  p.  m.,  three  hours 
and  ten  minutes  after  feeding  the  first  porphyry  charge, 
the  furnace  began  to  show  signs  of  distress,  and  at  6 130 
p.  m.  slag  and  matte  ceased  to  run.  The  furnace  was 
allowed  to  cool  down  and  the  end  jacket  removed.  A 
section  was  cut  down  on  the  chilled  material,  and  the 
following  noted:  The  unfused  porphyry  was  found  to 
occupy  a  space  extending  from  some  six  inches  below 
the  tuyeres  to  the  same  distance  above  the  bosh  line, 

222 


G.  F.  BEARDSLEY. 

a  thickness  of  about  2  feet  in  the  middle  of  the  furnace 
and  2  feet  6  inches  to  3  feet  against  the  jackets.  Above 
this  the  .unfused  portion  of  the  charge  extended  to  the 
feed-floor. 

A  portion  of  the  unfused  porphyry  was  broken  out 
and  carefully  separated  into  white  unfused  porphyry 
and  interstitial  slag,  and  analyzed,  with  the  following 
result : 

SiOa  FeO  CaO       A12O3  ZnO 

Porphyry  flux 77.30  2.75  0.63  15.20  

Unfused  porphyry   81.80  4.81  0.91  11.45  

Interstitial  slag 57.70  23.01  4.09  15.33  

Free-running  furnace  slag....  33.30  48.75  5.10        7.20  4.41 

The  viscid  high  temperature  interstitial  slag  re- 
mained near  where  it  was  formed,  and,  blocking  the  air 
passages  through  the  porphyry  flux,  cut  off  the  blast 
from  the  upper  part  of  the  charge.  Later  experiments, 
in  conjunction  with  quartz,  proved  its  entire  unsuita- 
bility  in  any  proportion.  The  aluminous  material  used 
at  Mount  Lyell  is  a  pyrophyllite  schist,  the  -aluminous 
mineral  being  a  bisilicate  and  very  finely  diffused 
through  the  r6ck.  The  aluminous  minerals  in  the 
quartz  porphyry  with  orthoclase  and  oligoclase  were 
trisilicates,  and  were  distributed  in  large  grains  and 
crystals. 

G.  F.  BEARDSLEY. 

New  York,  Oct.  10,  1904. 


223 


CONTRIBUTION  BY  LEWIS  T.  WRIGHT. 

The  Editor: 

Sir — Having  given  considerable  attention  to  the 
smelting  of  raw-sulphide  ore,  with  hot  blast  and  without 
coke,  at  Keswick,  I  am  in  a  position  to  answer  many  of 
the  questions  you  submitted  to  me  a  year  ago. 

Pressure  of  business  has  not  given  me  time  to  attend 
to  this  matter  until  now,  and,  if  not  too  late  for  your 
purpose,  I  will  give  you  a  summary  of  my  experience. 
The  time  at  my  disposal  even  now  does  not  permit  of 
going  into  the  subject  with  much  theoretical  detail,  and  I 
must  be  content,  therefore,  with  a  brief  recapitulation 
of  facts. 

The  ore  is  cupriferous  iron  pyrite,  rich  in  sulphur  and 
free  from  gangue.  The  first  practice  was  to  roast  the 
coarse  ore  in  large  heaps.  This  practice  was  carried  out 
on  such  a  scale  that  it  was  found  economical  to  load 
the  roasted  ore  into  railway  cars  by  means  of  steam- 
shovels.  The  fine  ore  was  roasted  sweet  in  mechanical 
furnaces  with  water-jacketed  arms  and  stirring  columns. 
This  type  of  furnace,  now  very  common,  was  first  de- 
veloped at  Keswick.  In  spite  of  an  early  failure  in  pyrite 
smelting,  Mr.  Fielding,  managing  director  of  the  Moun- 
tain Copper  Company,  remained  convinced  that  the 
practice  was  economically  possible,  and,  therefore,  en- 
couragement and  impulse  were  given  by  the  board  of 
directors  to  our  efforts  to  increase  the  amount  of  raw 
sulphide  smelted  and  to  reduce  the  use  of  coke.  About 
three  years  ago  the  heap-roasting  of  the  coarse  ore  was 
finally  abandoned,  and  it  was  smelted  direct  in  its  raw 
condition ;  later,  the  fine  ore  was  no  longer  roasted,  but 
also  was  smelted  raw. 

Your  first  question  asks :   "What  types   of  ore   are 

224 


LEWIS  T.  WRIGHT. 

suited  to  the  process?"  My  experience  only  relates  to 
those  containing  iron  and  sulphur,  and  these,  when 
smelted  with  a  suitable  flux,  certainly  can  be  smelted 
raw  without  the  use  of  coke  and  with  a  satisfactory  de- 
gree of  concentration. 

Your  second  question,  "Is  hot  blast  advisable?"  I 
can  answer  in  the  affirmative.  Several  years  ago,  whilst 
studying  the  question  of  hot  blast,  I  had  occasion  to 
converse  on  the  subject  with  an  eminent  metallurgist. 
His  opinion  was  distinctly  unfavorable  to  the  use  of  hot 
blast,  on  the  ground  that  it  was  not  logical  to  employ  a 
roundabout  process,  to  burn  fuel  outside  the  furnace  in 
heating  the  blast,  and  then  to  conduct  the  heated  air 
(with  inevitable  loss  of  efficiency)  to  the  furnace,  when 
the  same  fuel  might  be  used  direct  in  the  furnace  and 
to  more  effect.  The  argument  impressed  me  for  the 
moment,  but  fortunately,  on  consideration,  it  occurred 
to  me  that  it  was  not  yet  proved  that  we  obtained  the  full 
efficiency  of  the  carbonaceous  fuel,  charged  into  the 
furnace  at  the  top,  and  that,  probably,  some  portion  of 
this  fuel  might  be  consumed  towards  the  top  of  the 
furnace,  and  before  it  reached  the  smelting  zone,  and 
thereby  partly  lose  its  effect. 

One  of  the  principal  objects  I  had  in  view  in  the 
use  of  hot  blast  was,  in  the  case  of  raw-sulphide 
smelting,  to  increase  the  concentration,  or,  in  other 
words,  to  increase  the  oxidation  so  as  to  obtain  a  higher 
grade  of  matte  in  the  first  operation.  Carbon  is  a  re- 
ducing element  and  is  counteractive  in  respect  to  con- 
centration and  oxidation.  If,  therefore,  we  could  elimin- 
ate the  carbon  from  the  furnace,  we  should  have  more 
of  the  oxygen  of  the  blast  left  for  the  oxidation  of  the 
sulphide  and  the  grade  of  the  resultant  matte  would 
be  higher.  I  determined  to  try  hot  blast,  and  my  early 
experiences  demonstrated :  first,  that  a  certain  quantity 
of  carbon,  consumed  outside  the  furnace  in  heating  blast, 
replaced  a  larger  quantity  charged  at  the  top  of  the 

225 


PYRITE  SMELTING. 

furnace  as  coke;  second,  that  there  was  a  marked  in- 
crease in  the  concentration ;  and,  third,  that  there  was  a 
great  improvement  in  the  running  of  the  furnace.  These 
experiences  fully  justify  the  answering  of  your  second 
question  in  the  affirmative. 

In  reply  to  your  third  question,  I  can  say  that  carbon- 
aceous fuel  in  the  furnace  can  be,  and  is,  entirely  elimin- 
ated in  the  smelting  of  raw-sulphide  ores  when  the  con- 
ditions permit  of  the  oxidation  of  the  iron  sulphide,  and 
the  slagging  of  the  oxidized  iron  at  a  certain  rate  per 
unit  of  time,  and  at  a  certain  proportion  per  unit  of 
charge. 

Your  fifth  question  I  would  answer  by  saying  that 
lime  is  as  useful  in  lowering  the  copper  content  of  the 
slags  in  the  case  of  smelting  of  raw,  as  in  the  case  of 
the  smelting  of  roasted  ores. 

Your  sixth  question,  as  to  the  percentage  of  zinc  that 
can  be  profitably  treated  in  the  charge,  is  difficult  to 
answer.  Zinc  is  as  troublesome  in  the  case  of  raw-sul- 
phide smelting  as  it  is  in  the  case  of  the  smelting  of  oxi- 
dized ores.  As  the  percentage  of  zinc  rises,  more  fuel 
must  be  used,  whether  the  ores  be  roasted  or  raw. 
Pyrite  containing  5  per  cent  zinc  can  be  smelted  with  hot 
blast  without  the  use  of  coke. 

The  answer  to  your  seventh  question,  as  to  the  de- 
sulphurization  attainable,  depends  very  much  upon  the 
nature  of  the  flux,  because  the  rapidity  of  the  oxidation 
varies  with  the  chemical  character  of  the  flux ;  80  per 
cent  of  the  sulphur  should  be  volatilized  as  SO2. 

Your  eighth  question,  as  to  the  possibility  of  the  ca- 
pacity of  a  furnace,  reminds  me  that  the  furnace  cam- 
paigns smelting  raw-sulphide  ore  entirely  without  the 
use  of  fuel  are  short.  The  furnace  in  its  running  period 
will  run  as  nicely  as  with  roasted  ore  and  coke,  but  when 
the  furnace  gets  into  bad  condition,  and  begins  to  slow 
down,  no  attempt  is  made  to  save  it  in  any  way  by  the 
use  of  coke ;  and  if  it  does  not  recover  of  itself,  it  must 

226 


LEWIS  T.  WRIGHT. 

be  tapped  out  and  another  furnace  started  in  its  place. 
The  limitations  of  the  process  must  be  the  economical 
ones,  and,  in  that  way,  I  would  answer  your  ninth  and 
tenth  questions. 

It  has  been  demonstrated  at  Keswick  that  the  use  of 
coke  can  be  entirely  eliminated  in  the  smelting  of  raw 
sulphide,  even  when  the  charge  contains  a  large  quan- 
tity of  slag,  converter  slag,  flue-dust,  and  furnace-clean- 
ing, if  the  flux  is  sufficiently  acid. 

It  may  appear  singular  that  raw-sulphide  smelting  has 
not  been  more  practiced  and  that  it  is  only  recently,  so 
to  speak,  that  iron  pyrite  is  being  smelted  with  its  own 
fuel.  It  is  true  that  an  appeal  to  theory  indicates  that 
the  oxidation  of  iron  pyrite  should  yield  enough  heat 
to  raise  the  temperature  of  its  smelting  products  to  a 
state  of  fusion ;  but  it  was  not  found  easy  to  put  theory 
into  practice.  It  is  really  easy  if  suitable  conditions  are 
present,  and  if  one  is  prepared  to  dig  out  a  furnace  at  a 
cost  of  $50,  rather  than  to  save  it  at  a  cost  of  several 
hundred  dollars'  worth  of  coke.  The  fact  is  that  in 
practice  the  heat  afforded  by  the  combustion  of  the 
pyrite  does  not  leave  very  much  margin  for  the  pyritic- 
smelting  process.  In  the  first  place,  one  must  recollect 
that  there  is  a  difference  between  carbon  and  sulphur  in 
respect  to  combustion.  It  is  possible  to  effect  the  oxida- 
tion of  carbon  in  a  furnace  without  the  use  of  any  ex- 
cess of  air.  This  is  not  the  case  with  sulphur  and  sul- 
phide, which  cease  burning  before  the  surrounding  at- 
mosphere is  exhausted  of  its  oxygen,  and  whilst  it  al* 
ready  contains  a  certain,  and  not  small,  percentage  of 
this  element.  The  sulphur  dioxide  forms  what  is  called 
an  extinctive  atmosphere,  and  when  it  has  reached  a 
certain  proportion,  or  tension,  say  about  12  per  cent, 
the  reaction,  S  +  O2=SO2,  ceases  entirely. 

From  a  reference  in  Roberts-Austen's  'Introduction 
to  the  Study  of  Metallurgy'  I  infer  that  Plattner  was 
aware  of  the  effect  of  this  limiting  atmosphere  in  the 

227 


PYR1TE    SMELTING. 

roasting  of  sulphide,  and  that  a  certain  excess  of  air 
must  be  employed.  I  have  had  the  opportunity  of  ob- 
serving this  limit  with  various  furnaces,  such  as  blast 
furnaces,  roasting  furnaces,  converters,  etc.,  and  have 
found  it  much  below  that  which  would  be  the  case  if 
no  excess  of  oxygen  were  required,  as  it  is.  Here  is  one 
reason  why  it  has  not  been  found  easy  to  reach  the 
smelting  temperatures  by  the  simple  oxidation  of  pyrite. 
Another  reason  that  comes  into  prominence  is  the  speed 
of  the  reaction.  In  practice  we  cannot  escape  from  the 
element  of  time,  an  element  respecting  which  the  chemi- 
cal reactions,  as  graphically  set  forth  in  our  text-books, 
are  silent. 

There  is  a  certain  working  temperature  necessary  to 
produce  the  minimum  flow  of  molten  material  from  our 
furnaces,  and  to  produce  and  maintain  this  working 
temperature  a  certain  minimum  amount  of  heat  must  be 
produced,  per  unit  weight  of  charge  per  unit  of  time.  If 
the  heat  production  in  unit  of  time  should  fall  below  this 
amount,  the  process  of  smelting  would  cease.  The  sub- 
stances we  employ  in  the  charge  must,  therefore,  pro- 
duce heat  at  a  certain  rate.  In  the  case  of  iron  blast- 
furnace practice,  it  has  been  shown  by  Lowthian  Bell 
how  the  heat  required,  per  unit  of  charge,  is  distributed 
to  meet  losses  of  heat  (by  radiation,  expansion  of  blast, 
tuyere  water,  fusion  of  slag,  and  in  escaping  gases),  and 
to  carry  on  the  chemical  reactions  of  the  furnace,  such  as 
the  reduction  of  the  ferric  oxide.  In  the  case  of  cold 
blast,  he  found  that,  per  unit  of  charge,  a. total  of  1.73 
Cal.  was  required.  Dividing  this  into  two  categories,  I 
find  that  0.79  Cal.  was  required  by  the  chemical  pro- 
cesses, and  0.94  Cal.  (and  in  case  of  very  high  furnaces 
and  hot  blast  as  low  as  0.67  Cal.)  for  the  physical  heat 
processes.  In  the  case  of  iron  smelting,  higher  tem- 
peratures are  required  than  with  copper.  For  the  pur- 
pose of  illustration,  let  us  suppose  that  the  chemical 
reactions  in  the  blast-furnace  are  neutral,  neither  yield- 

228 


LEWIS  T.  WRIGHT. 

ing  nor  consuming  heat.  In  that  case  about  0.7  Cal.  per 
unit  weight  of  charge  should  provide  for  all  heat  re- 
quirements, and  keep  the  charge  melted  and  flowing. 
Since  one  unit  weight  of  carbon  gives  8.08  Cal.,  0.083 
weight  unit  of  carbon  will  give  0.67  Cal. ;  10  per  cent  of 
coke  (containing  83  per  cent  carbon)  burnt  to  CO2  will 
furnish  the  heat  for  the  work  to  be  done,  supposing  that 
the  chemical  reactions  in  the  furnace  are  neutral,  and 
that  we  require  for  copper  furnaces  the  same  degree  of 
heat  as  is  required  by  iron  blast-furnaces.  FeS  gives 
on  combustion  1.29  Cal.  per  weight  unit.  A  charge  of 
FeS  would  give  the  required  heat  of  0.67  Cal.,  if  0.52 
weight  unit  of  the  FeS  were  completely  oxidized  per 
unit  of  charge.  The  point  in  practice  is  to  get  the  iron 
sulphide  to  oxidize  at  a  sufficiently  rapid  rate.  If  the 
conditions  are  not  favorable  to  the  production  of  this 
rate,  naturally  the  operation  will  fail. 

I  have  not  enough  information  to  be  able  to  name 
with  the  same  degree  of  certainty,  as  in  the  case  of  iron 
blast-furnace  practice,  the  amount  of  heat  required  per 
unit  of  charge  to  carry  on  the  copper-smelting  operation. 
The  matter  is  further  complicated  in  the  case  of  iron 
pyrite  because  we  do  not  know  just  how  much  heat  is 
produced  by  the  oxidation  of  iron  pyrite,  and,  secondly, 
we  do  not  know  in  what  manner  the  sulphur  is  burned. 
One-third  of  the  sulphur  of  iron  pyrite  is  volatilized 
below  its  melting  point.  This  sulphur  escapes  at  the  top 
of  the  furnace,  making  a  hot  top,  and  does  not  produce 
its  full  value  in  the  smelting  operation.  We  all  know, 
hov/ever,  that  we  can  smelt  a  charge,  consisting  chiefly  of 
roasted  ore,  with  less  than  10  per  cent  coke  with  cold 
blast.  Ten  per  cent  of  coke  containing  83  per  cent  car- 
bon furnishes  0.67  Cal.  per  unit  weight  of  charge.  We 
ought  not  to  require  so  much,  judging  from  iron  blast- 
furnace practice.  FeS  gives  per  unit  weight  1.29  Cal., 
therefore,  if  we  could  burn  0.52  weight  unit  of  FeS  per 
unit  weight  of  charge,  and  could  consume  this  propor- 

229 


PYRITE    SMELTING. 

tion  of  the  charge  at  a  sufficient  rate,  and  slag  the  iron, 
the  process  should  go  on. 

I  have  no  experience  with  pyrrhotite,  but  on  referring 
to  the  interesting  account  given  by  Mr.  Freeland,  of 
Ducktown,1  in  his  case,  I  find  that  0.292  Fe  went  to 
slag,  and  0.165  S  went  to  SO2  per  unit  of  charge.  I 
will  assume  the  total  of  these  two  components,  that 
is,  .457,  to  be  calorifically  equal  to  FeS.  Thus  0.457 
by  1.29  Cal.  =  0.589  Cal.  generated  per  unit  of  charge. 
That  does  not  seem  to  be  quite  enough,  and  I  am,  there- 
fore, not  surprised  to  find  that  0.023  weight  unit  of  car- 
bon was  also  consumed.  This  quantity  is  calorifically 
worth  0.023  by  8.08  or  0.186  Cal.,  or  in  all  a  heat  pro- 
duction of  0.775  Cal.  per  unit  weight  of  charge,  which, 
from  comparison  with  iron  smelting  practice,  should 
be  enough.  In  our  case  at  Keswick  we  can  smelt  raw 
sulphide  without  coke  when  about  0.21  of  iron  goes  to 
slag  and  0.24  of  sulphur  goes  to  SO2  per  unit  of  charge, 
and  we  use  o.io  Cal.  in  heating  the  blast. 

I  do  not  know  the  calorific  value  of  pyrite.  One-third 
of  the  sulphur  volatilizes  below  the  smelting  temperature 
and  its  heating  effect  is  mostly  lost  in  the  gases.  If  we 
give  to  the  FeS  of  the  FeS2  its  value  of  1.29  Cal.,  and  to 
the  second  atom  of  sulphur  one-third  of  its  calorific 
value  as  an  element,  we  have  in  all  for  the  0.45  unit  oi 
pyrite : 

0.43  FeS  @  1.29  Cal 0.55  Cal. 

0.12  S        @  2.2    Cal.  x  % 0.09     " 

Hot  blast    .  .  0.10     " 


Total,  0.74  Cal. 

produced  per  unit  weight  of  charge,  not  allowing  any- 
thing for  the  heat  of  combination  of  FeO  and  SiO2. 

I  hope  I  shall  not  be  criticised  for  being  too  approxi- 
mate in  my  estimates  of  the  heat  requirements  of  the 
blast-furnace,  but  we  have  no  means  yet  of  arriving  at  a 
very  exact  figure.  I  did  get,  however,  a  vast  amount  of 

i  See  page  108. 

230 


LEWIS  T.  WRIGHT. 

help  and  encouragement  when  trying  to  find  out  how 
much  might  be  reasonably  expected  to  do  the  work.  A 
charge,  chiefly  of  oxidized  ores,  does  smelt  with  an 
amount  of  carbon  equivalent  to  0.7  Cal.  per  unit  weight 
of  charge  and  less.  No  allowance  has  been  made  in 
the  above  estimates,  which  are  confessedly  approximate 
(and  only  employed  for  the  purpose  of  focusing  the 
subject  on  a  point  of  view  I  found  of  great  help),  for 
the  heat  of  combination  between  FeO  and  SiO2.  There 
is  the  strongest  reason  for  believing  that  this  source  of 
heat  is  important;  so  important  that  unless  the  silica 
used  as  flux  be  sufficiently  acid,  and  free  and  not  com- 
bined, the  pyritic  process  will  not,  in  our  experience,  go 
on  unaided  by  coke,  and  then  the  concentration  is  un- 
satisfactory. In  cases  where  the  only  flux  available  is 
one  mainly  consisting  of  combined  silica,  a  compromise 
process  employing  a  certain  proportion  of  the  ore  in  a 
roasted  form  must  be  adopted.  I  found  great  aid  in 
my  efforts  by  keeping  in  mind  that  there  was  a  cer- 
tain minimum  heat  production  necessary  per  unit  of 
charge  to  keep  the  charge  melting  and  running,  and  that 
it  was  somewhere  about  0.70  Cal.  per  unit  weight,  and 
also  that  there  was  a  certain  minimum  weight  to  be 
smelted  in  a  given  time.  The  rate  of  chemical  change 
had  to  be  equal,  therefore,  to  so  many  calories  per 
second. 

It  is  impossible  for  me  to  leave  this  subject  without 
expressing  my  indebtedness  to  the  work  of  Mr.  Robt. 
Sticht,  of  Mt.  Lyell,  who  is  the  practical  pioneer  of 
pyrite  smelting,  so  far  as  I  am  concerned,  because  his 
work  has  been  always  an  example  and  incentive  to  me. 
In  carrying  out  this  work  at  Keswick,  I  was  ably  as- 
sisted by  Mr.  A.  S.  Haskell  and  Mr.  J.  A.  Balch,  re- 
spectively superintendent  and  assistant  superintendent 
of  the  smelter  there. 

LEWIS  T.  WRIGHT. 

231 


CONTRIBUTION  BY  CHARLES  S.  PALMER. 
The  Editor: 

Sir — The  information  on  pyrite  smelting,  accumulated 
from  the  columns  of  this  Journal,  is  calculated  to  im- 
press thoughtful  practice  everywhere.  It  represents  a 
body  of  timely  technical  contribution  almost  unparalleled 
in  the  history  of  metallurgy.  Indeed,  no  new  process, 
involving  so  much  that  is  valuable  and  untried,  has  ever 
reached  approximate  success  so  directly  and  quickly. 
Its  principles  are  older  than  the  range  of  any  living 
metallurgist ;  its  field  is  broader  than  the  tuyere  area  of 
the  blast  furnace.  All  smelter  men  are  watching  with 
interest  the  mistakes,  no  less  than  the  success  of  this 
method,  for  there  is  a  pathology  as  well  as  a  normal 
physiology  of  the  pyrite  blast;  and  the  careful  dissec- 
tion of  the  frozen  charge  has  shown  much  of  the  prob- 
able cause  of  strangulation.  The  collective  comment  of 
the  papers  comprise  a  composite  monograph  which  is 
occasion  for  congratulation.  But  we  should  not  infer 
from  this  that  all  the  incidental  questions  are  answered ; 
so  far  from  this  is  the  real  state  of  the  case  that  one  may 
say  that  not  only  are  some  of  the  problems  not  solved, 
but  some  are  not  even  stated.  The  convenient  analysis 
of  that  which  has  been  accomplished  would  recognize 
two  groups  of  topics;  namely,  first,  the  points  which 
seem  to  have  been  established  by  general  observa- 
tion and  experience;  and,  second,  the  points  which  are 
still  undetermined.  In  the  first  group  I  would  enumer- 
ate :  The  use  of  hot  blast ;  the  heat  obtained  from  the 
burning  of  FeS;  the  need  of  much  blast  (oxygen),  and 
the  value  of  free  silica.  Mr.  Lang  has  done  a  service  in 
reiterating  the  three  phases  of  pyrite  smelting,  namely, 
the  heat-making,  the  slag-making  and  the  matte-mak- 
ing ;  and  it  should  be  remembered  that  the  blast  furnace 

232 


CHARLES   S.   PALMER. 

represents  the  seat  of  war  of  many  conditions  which  find 
their  equilibrium  in  the  temperature  and  fluidity  of  the 
products  escaping  at  the  throat  and  at  the  spout  ;  none 
of  these  conditions  can  be  changed  without  affecting  all 
the  rest.  One  writer  has  commented  on  the  wonderful 
way  in  which  the  blast  furnace  selects  its  own  slag.  It 
is  true,  everything  in  nature  is  wonderful;  but  beyond 
this  it  would  be  seven  times  more  wonderful  if  the 
furnace  did  not  under  any  conditions  select  its  own  slag 
and  matte  in  accordance  with  the  energy  (heat)  and  the 
flux  furnished.  This  point  of  interlocked  equilibrium 
of  all  parts  and  functions  must  be  constantly  borne  in 
mind  —  the.  furnace  is  a  physiological  unit. 

It  is  a  fortunate  matter  that  we  should  have  learned 
the  value  of  hot  blast.  The  testimony  seems  conclu- 
sive that  it  is  of  advantage  in  saving  coke  and  in  forc- 
ing silica  into  the  slag,  especially  on  ore  lean  in  pyrite. 
How  the  blast  shall  be  heated  is  a  matter  of  local 
economy. 

The  heat  is  produced  from  the  burning  of  the  sulphur 
and  also  of  the  iron  of  the  pyrite;  for,  while  sulphur 
alone  furnishes  but  little  heat,  yet  it  may  be  just  enough 
to  raise  the  charge  above  the  danger  limit.  The  com- 
paratively small  quantity  of  free  sulphur  in  flue-dust 
would  indicate  that  most  of  it  is  consumed  in  the  furnace 
to  sulphur  dioxide. 

The  need  of  free  silica  in  absorbing  the  oxidized  iron 
is  clearly  emphasized.  The  lesson  that  this  should  be 
auriferous  quartz,  or  the  like,  has  been  well  shown  in 
lining  for  converter  practice. 

Among  the  second  class  —  the  unanswered  questions  — 
may  be  enumerated  :  The  copper  minimum  in  the 
matte;  the  heat  of  the  reactions: 

2FeS2  +  502  =  2FeO  +  4SO2, 


CaO  +  SiO2  =  CaSiO3  ; 

233 


PYRITE  SMELTING. 

and  the  condition  of  zinc  oxide  and  aluminum  oxide  in 
the  slag,  etc.  The  question  as  to  the  amount  of  copper 
required  to  hold  the  precious  metals  in  the  matte,  and 
the  correlated  question  as  to  the  influence  of  infinitesimal 
quantities  of  tellurium,  bismuth,  arsenic,  antimony,  and 
other  similar  value-thieves,  as  quoted  by  Peters  from 
Pearce,  are  curiously  answered  by  most  of  the  catechists. 
One-half  per  cent  is  a  very  small  piece  of  soap  for  so 
large  a  hand.  There  is  more  yet  to  come  from  this 
problem.  As  to  the  thermo-chemistry  of  the  equation, 
as  indicated,  there  is  no  excuse  in  this  age  of  science, 
and  endowment  kings  that  we  do  not  have  the  exact 
knowledge  of  all  the  more  important  metallurgical  ther- 
mal constants.  That  the  heat-toning  of  the  reaction, 
represented  by  each  equation  herewith  given,  is  con- 
siderable cannot  be  doubted. 

The  question  as  to  the  condition  of  zinc  oxide  in  the 
slag  has  several  aspects.  Lloyd  says  that  the  zinc  slag 
may  melt  at  as  low  a  temperature  as  the  corresponding 
iron  slag,  though  it  will  be  less  fluid.  Peters  mentions  a 
slag  that  was  fluid,  though  high  in  zinc  and  earths  and 
low  in  iron ;  figuring  the  alumina  as  an  acid,  the  slag  was 
a  bi-silicate.  Others  speak  of  zinc  compounds  as  float- 
ing in  the  slag  much  as  snow  floats  in  ice-water.  This 
might  easily  be  a  case  of  mass  suspension.  In  fluid 
homogenous  zinc  slags  the  zinc  may  be  a  silicate,  an 
alumino-silicate,  an  aluminate,  or  a  mutual  solution  of 
these. 

As  to  the  rule  of  alumina,  I  have  discussed  this  from 
one  aspect  in  another  issue  of  this  Journal  (March  2, 
1905,  page  420).  But  there  is  another  side  rich  in  possi- 
bility. It  seems  a  common  custom  (note  the  experience 
of  Bretherton)  to  figure  alumina  as  two-thirds  of  the 
silica ;  but  this  needs  definition.  Alumina  may  react  as 
the  met-aluminate,  or  as  the  normal  aluminate;  and  it 
may  be  compared  with  metasilicic  acid  or  normal  silicic 

234 


CHARLES  8.   PALMER. 

acid.  In  these  cases  it  would  function  respectively  as 
2  to  3,  2  to  5,  i  to  I,  and  4  to  5.  But  in  view  of  the  great 
tendency  to  the  formation  of  alumino-silicates  on  the 
one  hand,  and  on  the  other  the  absence  of  calcium  alum- 
mates  or  met-aluminates  as  such  (though  ferrous  met- 
aluminates  are  known  in  ismorphous  iron  mixture), 
there  is  another  view  that  is  broader  and  more  probable, 
and  to  which  I  will  revert  later. 

Magnetite  seems  to  be  a  standing  nuisance.  It  de- 
serves a  separate  study;  meanwhile  we  should  remem- 
ber that  it  is  not  a  simple  oxide,  but  a  'salt  oxide'  — a 
salt  compound  of  a  lower  and  a  higher  oxide  of  iron. 

But  the  richness  of  this  bill  of  fare  must  not  make  one 
a  metallurgical  gourmand.  If  one  is  challenged  to  pro- 
duce some  distinct  product  of  pyrite-smelting  theory 
and  practice,  he  need  only  refer  to  the  actual  concen- 
tration of  matte.  This  is  practical  in  the  regular  copper 
furnace  with  high  fuel  by  those  who  know  how  to  do  it. 

In  discussion,  fact  is  the  basis ;  but  it  will  be  well  to 
awake  from  the  lethargy  that  comes  of  too  close  scrutiny 
of  detail.  Let  us  look  at  the  question  fairly,  as  we 
ask :  What  is  the  broad  teaching  of  this  phase  of  blast- 
furnace practice?  There  is  a  growing  tendency  among 
matte-smelters  to  reject  the  theory  of  any  single  and 
constant  slag  content.  Such  may  occur  as  exceptional. 
But,  on  the  other  hand,  we  have  in  well-attested  practice 
the  gradual  swinging  from  high  iron  and  low  lime  to 
high  lime  and  low  iron.  Where  is  the  limit  here?  It 
looks  as  though  we  are  dealing  with  a  mixed  solution  and 
intersolution  of  several  accommodatingly  soluble  media. 
The  fusibility  of  slags  is  only  partly  worked  out ;  but  be- 
yond that,  the  question  of  the  mutual  solubility  of  sev- 
eral slags  calls  for  measurement.  This  does  not  ignore 
the  probable  calcium  meta-silicate  (bi-silicate)  nor  the 
ferrous  ortho-silicate  (uni-silicate) ;  but  it  does  put  the 
question  on  a  broader  basis,  and  it  also  propounds  cer- 

235 


PYR1TE    SMELTING. 

tain  comparatively  simple  laboratory  experiments  on 
mutual  solubility  which  it  is  not  to  the  credit  of  metal- 
lurgy to  neglect  longer.  Thus,  if  a  molten  flux  contains 
two  fusible,  non-ionizable  and  mutually  soluble  salts 
(which  we  will  call  A  and  B),  there  are  four  units  to  con- 
sider, namely :  A  and  B  themselves,  the  solution  of  A 
in  B  and  the  solution  of  B  in  A.  But  if  there  is  ioniza- 
tion,  then  new  possibilities  and,  presumably,  new 
limitations  would  appear,  which  must  be  investigated 
on  the  basis  of  the  well-known  phase-rule  of  Gibbs. 

The  essays  on  'Pyrite  Smelting/  when  published  to- 
gether, will  find  a  place  on  the  desk  of  every  working 
metallurgist ;  they  comprise  a  storehouse  of  specialized 
fact  and  practice  not  excelled  in  this  generation . 

CHARLES  S.  PALMER. 
New  York,  March  14,  1905. 


236 


CONTRIBUTION  BY  HIRAM  W.  HIXON. 
The  Editor: 

Sir — Pyrite  smelting  has  been  the  subject  of  much 
discussion  in  The  Engineering  and  Mining  Journal,  and 
under  certain  peculiar  conditions,  which  are  purely  local, 
it  is  entitled  to  be  called  a  process,  as  distinguished  from 
ordinary  blast-furnace  smelting. 

All  blast-furnace  smelting,  even  lead  smelting  with 
the  use  of  14%  of  coke,  will  eliminate  some 
sulphur  from  the  charge,  which  passes  off  with 
the  flue  gases,  and  some  iron  must  be  liberated 
and  go  into  the  slag  as  a  result.  Not  more  than 
70%  of  the  sulphur  on  a  lead  charge  can  be  ac- 
counted for  by  the  matte  produced  under  conditions 
when  a  heavy  reducing  action  is  indicated  by  the  pro- 
duction of  a  small  amount  of  speiss  along  with  the  lead- 
copper  matte.  This  indicates  that,  even  in  the  presence 
of  so  much  as  14%  of  coke,  sulphides  do  burn,  and,  once- 
combined  with  oxygen,  they  are  separated  by  the  re- 
ducing action  of  the  fuel,  or  the  gases  of  partial  combus- 
tion. 

The  proper  conditions  for  the  greatest  amount  of  re- 
duction, or  the  reverse,  the  greatest  amount  of  oxidation, 
in  a  blast-furnace  are  so  much  affected  by  the  method 
of  feeding  and  the  arrangement  of  the  particles  in  the 
furnace  that,  without  taking  these  conditions  into  con- 
sideration along  with  the  volume  of  blast  per  minute, 
there  is  no  certainty  what  kind  of  a  slag  will  result.  For 
example,  suppose  a  furnace  is  running  on  a  charge  pro- 
ducing 30%  copper  matte,  and  making  a  slag  containing 
30%  SiO2  and  0.3%  Cu.  The  percentage  of  fuel  may  be 
anything  from,  say,  3  to  12,  depending  upon  the  amount 
of  pyrite  on  the  charge,  and  also  the  amount  of  copper 

237 


PYRITE    SMELTING. 

and  the  degree  of  roast,  if  any.  Now,  suppose  we  speed 
up  the  blowers  or  put  on  more  blast  in  any  suitable  way ; 
we  would  notice  the  following  results :  (i)  The  tonnage 
smelted  will  be  increased,  (2)  the  matte  will  contain  a 
higher  percentage  of  copper,  and  (3)  the  slag  will  con- 
tain more  iron,  less  silica  and  more  copper,  not  in  exact 
proportion  as  the  blast  is  increased,  but  governed  by  it. 
All  of  these  conditions  are  changed  by  simply  increasing 
the  blast  volume  per  minute. 

Pressure  does  not  mean  anything  except  resistance, 
and  it  may  be  caused  by  charge  burden  or  slag  in  the 
tuyeres,  or  it  may  mean  that  the  tuyeres  are  too  large 
or  too  small.  After  these  conditions  are  adjusted  to  an 
equilibrium,  suppose  we  change  the  method  of  feeding 
from  an  even  distribution  of  fine  and  coarse  particles  to 
placing  the  coarse  pieces  near  the  wall  and  the  fine  in 
the  center  of  the  shaft.  The  result  will  be  a  further  ox- 
idation of  sulphides,  resulting  in  a  further  increase  of 
iron  in  the  slag  and  a  corresponding  decrease  of  silica. 
The  percentage  of  copper  will  increase  in  both  the  slag 
and  matte,  and  the  amount  of  matte  produced  will  de- 
crease. All  of  these  changes  of  composition  of  the  fur- 
nace products  will  be  affected,  not  by  any  change  of 
charge  or  fuel,  but  by  increasing  the  volume  of  blast  and 
altering  the  arrangement  of  the  particles  composing 
the  charge.  The  furnace  will  not  continue  to  run  for 
long  without  crusts  forming  on  the  walls,  and  this  may 
increase  at  one  end  or  on  one  side  and  diminish  or  en- 
tirely disappear  on  the  other,  for  the  passage  of  the 
furnace  gases  is  so  restricted  that  it  results  in  blow- 
holes; and  these  affect  the  oxidation  to  such  an  extent 
that  it  frequently  happens  that  two  furnaces  running 
on  the  same  charge  will  produce  slags  varying  3  or  4% 
SiO2  or  Fe,  and  mattes  varying  as  much  as  10%  in  copper 
content. 

In  this  manner  we  may  vary  the  action  of  the  furnace, 
and  if  we  continue  to  increase  the  blast  we  finally  ar- 

238 


HIRAM  W.  HIXON. 

rive  at  a  point  where  the  copper  losses  in  the  slag,  to- 
gether with  the  precious  metals  or  others  if  there  be 
any,  would  be  too  great  to  allow  a  further  concentration 
on  a  commercial  basis.  The  slag  losses  increase  much 
faster  than  the  grade  of  the  matte,  and  while  we  may 
have  increased  the  copper  in  the  matte  from  30  to  40% 
the  slag  will  have  increased  from  0.3  to  0.6%  or  more. 
All  this  goes  to  show  that  the  pyrite  is  not  the  only 
thing  that  is  oxidized ;  copper  and  nickel  and  all  the  as- 
sociated metals  in  the  charge  get  their  share  of  oxida- 
tion, and  that  is  opposed  to  the  collecting  action  of  the 
matte.  Slags  formed  under  such  conditions  resemble 
slags  made  in  the  copper  converter;  they  are  foul  and 
contain  a  considerable  percentage  of  peroxidized  iron, 
which  renders  them  magnetic.  They  will  not  decom- 
pose with  acids  without  fusion  with  an  alkali  carbonate. 

The  remarkable  effect  of  reversing  the  distribution  of 
the  pieces  composing  the  charge  is  shown  in  lead  smelt- 
ing, where  it  has  been  demonstrated  that  it  is  absolutely 
necessary  to  feed  the  fine  to  the  walls  and  the  coarse 
to  the  center  in  order  to  get  the  reduction  necessary 
to  prevent  excessive  oxidation  and  loss.  About  the  y-ear 
1883  the  flat-top  lead  furnace  was  introduced  in  nearly 
all  the  Colorado  smelters,  and  at  first  they  were  fed 
through  a  narrow  thimble ;  but  in  every  case  this  had  to 
be  abandoned  because  it  had  the  effect  of  placing  the 
entire  charge  in  the  center  until  it  sank  below  the  end 
of  the  thimble,  releasing  the  coarse  pieces,  which  rolled 
to  the  sides  and  ends  of  the  shaft,  while  the  fine  all  set- 
tled down  in  the  center.  The  blast  naturally  passed, 
up  through  the  coarse  pieces  and  caused  over-fire  be- 
hind the  thimble,  the  reduction  stopped,  and  almost  im- 
mediately the  bullion  production  decreased  to  an  alarm- 
ing extent.  These  were  'pyrite  smelting'  conditions 
applied  to  lead  smelting,  and  the  reverse  of  what  should 
have  been. 

The  feeding  was  then  done  by  shoveling  the  coarse 

239 


PYRITE    SMELTING. 

to  the  center  and  the  fine  to  the  wajls,  forcing  the  car- 
bon monoxide  formed  at  the  tuyeres  to  penetrate  the 
charge  to  the  center  and  act  as  a  reducing  agent  all 
the  way  tip  through  the  charge.  Later,  when  automatic 
feeding  from  a  car  was  introduced,  it  was  found  that  the 
charge  had  to  be  dumped  so  that  it  would  be  highest 
against  the  walls,  and  the  large  pieces  could  roll  to  the 
center,  preserving  the  conditions  as  described.  If  at  any 
time  a  number  of  charges  were  dumped  in  the  center 
the  conditions  would  become  reversed,  over-fire  would 
start,  and  bullion  production  would  stop  or  decrease. 

The  bell-and-hopper  feed  of  the  iron  blast-furnace 
is  admirably  suited  for  a  round  furnace,  as  it  forces  the 
stock  to  the  outside  and  leaves  the  center  lower,  so  that 
the  pieces  arrange  themselves  in  the  order  required  for 
reduction;  but  this  method  of  feed  is  not  suited  for  rec- 
tangular furnaces  for  lead  smelting,  and  is  not  required 
for  copper  smelting,  as  was  demonstrated  at  Aguas 
Calientes,  Mexico,  in  1896. 

In  pyrite  smelting,  dumping  the  charge-cars  from  the 
side  results  in  the  coarse  pieces  going  to  the  opposite 
side  and  the  fine  landing  in  the  center,  especially  if  the 
surface  of  the  charge  is  5  or  6  ft.  below  the  level  of  the 
feed-door.  The  result  is  that  there  is  a  ring  of  fire  and 
escaping  gases  around  the  edges  of  the  charge,  and  the 
center  is  perfectly  dead.  I  saw  this  strikingly  illustrated 
about  two  years  ago  at  the  works  of  the  Tennessee  Cop- 
per Company,  where  a  man  fell  into  a  furnace  smelting 
600  tons  per  day.  He  picked  himself  up  and  walked 
around  on  the  dead  center  and  tried  to  climb  out,  until 
the  blast  was  shut  off  and  a  ladder  lowered  to  him,  when 
he  climbed  out  within  reach  of  men  at  the  feed-door. 
The  only  injuries  he  sustained  were  to  his  hands  and 
face  and  parts  of  his  body  where  his  clothing  had 
burned.  It  was  thought  that  his  lungs  would  be  injured 
but  this  was  not  the  case.  Afterward  it  was  found,  by 
putting  in  pieces  of  paper,  that  there  was  a  down  draft 

240 


HIRAM  W.  HIXON. 

of  air  in  the  center  induced  by  the  blast  around  the  sides. 
As  the  carbon  monoxide  did  not  penetrate  to  the  center 
of  the  charge  it  could  not  exert  any  reducing  action,  and 
therefore  the  conditions  for  oxidation  and  concentration 
of  matte  were  present  and  active,  resulting  in  making 
a  40%  matte  out  of  the  3%  ore. 

Under  all  such  conditions  of  high  concentration  by 
oxidation,  the  resulting  slags  are  much  higher  than  they 
would  be  if  the  conditions  of  blast,  fuel  and  feeding  were 
reversed  to  produce  the  conditions  necessary  for  reduc- 
tion. The  commercial  aspect  of  the  case  is,  however, 
governed  by  local  conditions,  and  depends  entirely  upon 
which  method  gives  the  greatest  net  return  from  the 
ore.  Some  men  argue  that  it  pays  better  to  waste 
metals  and  save  coke  than  the  reverse.  However  this 
may  be,  I  note  where  one  company  turned  a  surplus 
into  a  deficit  by  following  the  plan.  It  would  appear 
that  a  dollar's  worth  of  coke  saved  is  not  worth  as  much 
as  two  dollars'  worth  of  metals  wasted. 

The  two-stage  operation  of  first  making  a  low-grade 
matte  12  to  20%,  re-smelting  and  concentrating  this  to 
35  or  40%,  and  re-smelting  the  slag  from  the  matte 
concentration  when  it  is  high  enough  to  justify  it,  seems 
to  be  the  best  plan  devised.  Trying  to  make  a  convert- 
ing grade  in  one  operation  results  in  too  high  slag  losses 
and  short  furnace  campaigns.  At  La  Aurora,  Mexico, 
a  middle  course  was  taken.  'A  6%  ore  containing  11% 
Zn  was  part  roasted  in  stalls  and  piles  and  smelted  with 
equal  part  of  green  'fine'  and  6.5%  coke.  The  resulting 
matte,  about  35%,  was  converted  and  the  converter-slag 
added  to  the  charge.  The  blast-slag  contained  10%  Zn 
and  0.6%  Cu.  The  high  copper  content  of  slag  was  due 
to  high  bias":  and  zinc,  otherwise  the  zinc  gave  no 
trouble.  An  ore  containing  zinc  will  make  a  higher  con- 
centration than  if  the  zinc  were  replaced  by  iron. 

The  degree  of  concentration  is  all  dependent  on  the 
blast,  the  fuel,  feeding,  and  the  amount  of  iron  in  the 

241 


PYRITE  SMELTING, 

ore.  An  ore  containing  a  small  percentage  of  iron  will 
make  a  higher  concentration — that  is,  more  tons  of  ore 
into  one  ton  of  matte — than  an  ore  containing  a  higher 
percentage  of  iron.  Hot  blast  may  be  a  benefit,  but  it 
is  a  luxury  that  at  many  plants  they  have  found  they 
can  get  along  without. 

It  is  a  difficult  point  to  define,  but  I  should  say  that 
pyrite  smelting  does  not  begin  until  the  slags  show  the 
characteristic  peroxidation  of  the  iron  as  evidenced  by 
chilled  samples  refusing  to  decompose  without  fusion. 
If  a  chilled  sample  will  not  give  white  silica  without 
fusion,  you  may  be  quite  sure  that  it  has  been  produced 
under  conditions  of  oxidation  characteristic  of  'pyrite 
smelting/ 

The  capacity  of  any  plant  smelting  raw  sulphides  with, 
say,  3%  coke  and  high  blast  is  less  than  half  its  capacity 
of  pile-roasted  ore  with  10%  coke  when  producing  the 
same  grade  of  matte  (35%  to  40%). 

HIRAM  W.  HIXON. 
Victoria  Mines.  Ont.,  April  4,  1905. 


242 


CONTRIBUTION  BY  S.  E.  BRETHERTON. 

The  Editor: 

Sir — Having  just  read  the  favorable  comments  on 
pyrite  smelting  and  the  use  of  hot  blast,  by  your  Mr. 
Charles  S.  Palmer,  in  The  Engineering  and  Mining  Journal 
of  March  30,  I  thought  it  an  opportune  time  to  add  a 
little  more,  through  your  valued  columns,  to  this  im- 
portant subject.  In  regard  to  the  amount  of  copper  nec- 
essary to  collect  the  gold  and  silver,  this  depends  on  the 
amount  of  zinc  with  which  the  metallurgist  has  to  con- 
tend: I  know  from  experience  that,  with  considerable 
zinc,  5%  Cu  in  the  charge  gives  much  cleaner  slag  than 
only  0.5%  Cu,  even  when  making  a  much  richer  matte 
in  Au  and  Ag,  and  smelting  the  same  character  of  ore. 

Alumina,  for  convenience,  can  be  classed  as  silica,  and 
I  prefer  to  limit  its  use  to  12%  in  the  slag.  To  be  exact, 
when  figuring  a  bi-silicate  slag  for  copper  smelting,  the 
formula  would  be :  2Al2O3+3FeO=48.8%  A12O3,  that  is, 
2O  in  the  acid  to  lO  in  the  base,  classing  the  A12O3  as 
an  acid,  which  corresponds  to  the  formula:  FeO+SiO2 
slag  =  45.696  SiO2;  or  CaO+SiO2  slag  =  51.9^ 
SiO2 ;  as  the  proportion  of  A12O3  in  the  slag  increases, 
the  amount  of  SiO2  should  be  reduced.  To  allow  theSiOa 
and  A12O3  together  to  get  above  the  bi-silicate  limit 
will  eventually  cause  trouble. 

A  silicious  slag  for  copper  smelting  seems  to  be  the 
most  suitable  for  concentration  and  clean  work.  Of 
course,  with  plenty  of  Cu  and  good  matte-fall,  the  dan- 
ger of  loss  is  lessened ;  first,  by  having  plenty  of  Cu  and 
matte  to  gather  value ;  and,  second,  by  the  fact  that 
there  is  a  smaller  proportion  of  slag  to  act  as  a  means 
to  carry  off  value. 

243 


PYRITE    SMELTING. 

An  acid  slag,  especially  when  low  in  Fe,  requires  more 
heat  than  a  basic  slag,  and  for  this  reason ;  it  is  neces- 
sary to  use  4  or  5%  coke  in  the  charge  in  hot-blast 
smelting,  to  avoid  accidents,  especially  when  there  is 
danger  of  trouble,  with  belting,  pulleys,  etc.,  as  in  the 
case  of  a  new,  small  plant  attempting  to  do  all  its  work 
with  one  engine  and  machinery  generally  poorly  ar- 
ranged. 

The  heat  applied  to  the  furnace  from  the  outside,  by 
means  of  hot  blast,  is  more  effective  for  economy,  rapid 
smelting,  and  other  advantages;  but  the  furnace  can- 
not be  banked  for  any  great  length  of  time  without  pre- 
paring for  it  by  first  adding  several  charges  with  extra 
coke.  These  extra  charges  should  consist  mostly  of 
slag  or  oxidized  ore,  on  account  of  the  extra  coke  (re- 
ducing agent)  added. 

The  metallurgist  of  a  custom  copper-smelter  often 
finds  himself  'between  the  devil  and  the  deep  sea';  he 
has  no  iron  except  as  a  sulphide,  and  that  in  limited 
amount,  which  compels  him  to  make  a  silicious  slag, 
high  in  lime.  To  avoid  trouble  with  this  character  of 
slag  (and,  perhaps,  accidents  with  poor  machinery)  he 
should  use  5  or  6%  coke  on  the  charge — nearly  one-half 
the  normal  amount  used  with  cold  blast.  On  the  other 
hand,  the  use  of  too  much  coke  prevents  the  necessary 
concentration  to  force  the  Fe  (which  he  must  have)  into 
the  slag,  and  the  elimination  of  impurities,  such  as  Zn, 
Pb,  As,  etc.,  which  should  not  be  allowed  to  enter  the 
matte. 

The  metallurgist  can  be  saved  much  trouble  and 
worry  by  having  the  capital  necessary  to  enable  him  to 
wait  for  proper  ore  mixtures,  and  to  repair  or  set  up 
proper  machinery  so  as  to  avoid  accidents ;  indeed,  im- 
portant parts  should  be  duplicated. 

S.  E.  BRETHERTON. 
Val  Verde,  Ariz.,  April  10,  1905. 

244 


CONTRIBUTION  BY  LEWIS  T.  WRIGHT. 

The  Editor: 

Sir — Seven  years  ago  the  ideal  of  the  metallurgist 
working  with  sulphide  copper  ore  was  to  roast  it  in  me- 
chanical roasting  furnaces,  after  such  preliminary  crush- 
ing as  was  necessary,  to  press  the  fine  calcines  into 
briquettes  and  smelt  these  with  coke.  To-day  we  are 
smelting  these  sulphide  ores,  coarse  or  fine  as  they  come 
from  the  mine,  with  no  other  combustible  than  the  iron 
and  sulphur  they  may  contain. 

The  chemistry  of  pyrite  smelting  is  the  chemistry  of 
iron  and  sulphur.  It  is  the  oxidation  of  this  iron  and 
sulphur  by  the  air  pumped  in  the  base  of  the  furnace 
that  provides  heat  required  to  maintain  the  tempera- 
ture of  the  furnace  at  that  degree  which  is  necessary  for 
the  digestive  process  of  pyrite  smelting. 

The  human  body  is  a  blast-furnace  and  its  tempera- 
ture must  be  maintained  at  a  living  grade  by  the  oxidiz- 
ing action  of  the  air  pumped  in  and  out  by  the  lungs ;  be- 
cause, if  the  production  of  heat  fall  below  the  amount 
required  to  compensate  for  loss  of  heat  by  radiation 
and  other  sources  of  loss,  its  temperature  will  fall  below 
the  initial  temperature  of  the  chemical  reactions ;  pro- 
duction of  heat  will  cease  and  the  body  will  'freeze  up/ 

An  interesting  study  in  pyrite  smelting  (and  by  pyrite 
smelting  I  mean  the  smelting  of  crude  sulphide  without 
carbon)  is  the  amount  of  air  required.  This  branch  of  the 
subject  has  been  too  much  neglected.  The  metallurgist 
in  charge  of  the  pyrite  blast-furnace  must  stand  literally 
with  one  eye  on  the  blower,  and  the  other  on  the  furnace 
with  its  charges,  its  slag  and  matte. 

The  blower  turns  should  be  as  closely  watched  and 

245 


PYRITE   SMELTING. 

recorded  as  any  other  of  the  incidents  of  the  operation. 
The  air  is  the  breath  of  life  of  the  furnace. 

The  heat  losses  are  considerable,  and  a  certain  tem- 
perature must  be  maintained  to  allow  the  slag  and  matte 
not  only  to  flow  out  of  the  furnace,  but  in  many  cases  to 
be  held  a  little  while  in  a  molten  state.  There  will  be, 
for  any  furnace,  a  certain  minimum  rate  of  heat  produc- 
tion required  to  maintain  this  minimum  degree  of  tem- 
perature, and  this  in  pyrite  smelting  demands  a  certain 
rate  of  oxidation  and  a  certain  supply  of  air. 

The  rate  of  heat  production  is  expressed  by  two  fac- 
tors, the  weight  of  charge  smelted,  and  the  proportion 
of  the  oxidizable  materials  in  the  charge  (the  iron  and 
sulphur)  oxidized.  The  former  is  the  rate  of  running,  or 
the  speed  of  the  furnace,  and  is  expressed  in  tons  per 
hour  or  day,  or  number  of  charges  per  hour  or  tons 
smelted  per  square  foot  of  furnace  area  per  24  hours. 
The  latter  factor  is  the 'concentration/ the  'sulphur  elimi- 
nation,' or  the  'oxidation/  The  product  of  the  two  fac- 
tors is  the  rate  of  heat  production,  and  this  can  also  be 
conveniently  expressed  in  terms  of  weight  or  volume 
of  air  or  oxygen  used  in  a  given  time. 

In  the  human  economy  the  air  which  is  inspired  with 
the  oxygen  content  of  20.8%  is  expired  with  16%  of 
oxygen.  The  efficiency  of  air  is  thus  in  the  human  blast- 
furnace not  very  high,  being  only  about  25%.  I  have 
been  at  some  pains  to  determine  its  efficiency  as  an 
oxidizing  agent  in  our  pyrite-smelting  practice,  and  have 
found  it  to  be  as  high  as  70  per  cent. 

It  is  now  time  to  discuss  the  amount  of  oxygen  or  air 
required  by  pyrite  in  its  oxidation.  The  pyrite  in  this 
process  is  the  fuel.  When  FeS2  is  heated  in  a  neutral 
atmosphere,  one-third  of  its  sulphur  volatilizes,  thus 
3(FeS2)— Fe3S4+S2.  It  is  said  that,  under  certain  cir- 
cumstances of  limited  oxidation,  one-half  of  the  sulphur 
is  recovered  as  such.  I  have  not  yet  had  an  opportunity 
of  confirming  this  statement,  the  belief  in  which  must 

246 


LEWIS  T.  WRIGHT. 

be  the  origin  of  the  metallurgist's  Volatile  atom/  In 
pyrite  work  we  do  see  signs  of  free  sulphur  in  the  fur- 
nace gases. 

The  amount  of  air  required  for  the  complete  oxida- 
tion of  pyrite  in  smelting  is  FeS2+5O=FeO+2SO2,  or 
120  parts  by  weight  of  pyrite  require  80  parts  by  weight 
of  oxygen,  or  I  Ib.  FeS2  requires  2-3  Ib.  oxygen. 

A  pyrite  furnace, with  area  at  tuyerelevelof43.75  sq.  ft. 
and  running  well,  smelts  its  charge  at  the  rate  of  n 
tons  of  total  burden  per  sq.  ft.  of  furnace  area  per  24 
hours,  or  20.05  tons  °f  charge  per  hour,  or  668.3  Ib.  per 
min.  The  amount  of  air  used  is  most  conveniently  dealt 
with  on  the  basis  of  the  minute.  I  take  as  an  example 
a  case  from  actual  practice.  The  charge  consists  of  py- 
rite containing  some  chalcopyrite,  the  requisite  fluxes, 
the  converter  slag  resulting  from  the  second  operation, 
and  flue  dust  in  proportion  as  normally  produced. 
The  pyrite  operation  is  ideal  and  there  is  no  coke  on  the 
charge.  The  FeS2  charged  (calculating  all  the  iron  in 
the  ore  as  FeS2)  is  at  the  rate  of343lb.  per  minute,  and  is 
close  to  50%  of  the  total  burden.  The  composition,  the 
texture  of  the  charge,  and  the  air  supply  are  properly 
adjusted  and  the  oxidation  is  high  in  consequence.  The 
degree  of  oxidation  of  the  FeS2  is  90%.  Thus,  343x0.9 
=308.7  Ib.  of  FeS2  being  oxidized  every  minute.  The 
furnace  gases  contain  12%  of  SO2  immediately  on  top 
of  the  charge.  Each  pound  of  FeS2  requires,  for  com- 
plete combustion,  2-3  Ib.  oxygen. 

A  pound  of  oxygen  is  contained  in  55  cu.  ft.  of  air 
at  72° F.  The  efficiency  of  the  air  is  70% ;  therefore, 
78.6  cu.  ft.  of  air  are  required  to  furnish  i  Ib.  of  oxygen. 
On  this  basis,  52.4  cu.  ft.  of  air  will  be  required  for  i  Ib. 
of  FeS2  oxidized;  308.7x52.4,  or  16.176  cu.  ft.  of  air  per 
min.,  are  therefore  required  by  this  furnace.  The  amount 
of  air  actually  measured  by  the  displacement  of  the 
blowers  was,  in  the  instance  I  cite,  found  to  be  16,985 
cu.  ft.  per  min.  In  this  case,  0.21  of  iron  and  0.24  of 

247 


PYRITE    SMELTING. 

sulphur  were  oxidized  per  unit  of  charge.  This  ex- 
presses the  degree  of  oxidation.  The  rate  of  oxidation 
was  308.7  Ib.  FeS2  per  minute. 

It  is  stated  that  I  kilogram  of  FeS2  when  oxidized  to 
Fe2O3  gives  2.253  calories.  Adjusting  this  value  to 
oxidation  to  FeO,  which  is  the  case  in  making  slag,  we 
have  as  the  heat  of  combustion  of  pure  pyrite  1.976 
calories. 

In  the  above-cited  case  the  pyrite  of  the  charge  was 
yielding  heat  at  the  rate  of  0.89  calorie  per  unit  weight 
of  charge.  To  produce  this  amount  of  heat  from  coke 
containing  93%  of  carbon,  uf%  would  have  been  re- 
quired. The  furnace  at  this  period  was  running  very 
fast,  because  it  was  very  hot ;  but  the  heat,  with  the  ex- 
ception of  the  small  amount  afforded  by  the  heated  blast, 
was  being  produced  from  the  pyrite. 

A  pyrite  furnace  is  doing  good  work  when  it  is  using 
per  min.,  for  each  sq.  ft.  of  area,  as  many  cu.  ft.  of  air 
as  there  are  days  in  the  year,  and  oxidizing  as  many 
pounds  weight  of  FeS2  per  minute  as  there  are  days  in 
the  week ;  and  when  the  furnace  gases  on  the  top  of  the 
charge  contain  as  many  per  cents  of  sulphur  dioxide  as 
there  are  months  in  the  year.  This,  though  it  may 
sound  cabalistic,  is  the  true  memoria  technica  of  the 
pyrite  smelter. 

LEWIS  T.  WRIGHT. 

Keswick,  Cal.,  May  I,  1905. 


248 


CONTRIBUTION  BY  P.  L.  MARSTON. 

The  Editor: 

Sir — I  have  read  with  much  interest  various  communi- 
cations on  sulphide  smelting-,  and  I  wish  to  give  my  ex- 
periences in  confirmation  of  some  of  the  views  already 
expressed. 

In  re-heated  blast  I  have  found  that  it  always  gives 
a  decided  advantage  over  cold-blast  practice,  even  where 
the  rise  in  temperature  is  a  relatively  small  one.  In 
one  instance  60°  made  a  very  noticeable  difference  both  in 
the  speed  ai.d  control  of  the  furnace.  At  the  plant  of  the 
Ouray  Smelting  Company  the  blast  was  heated  by  the 
waste  gases  from  the  furnace.  A  number  of  horizontal 
convolutions  of  the  blast-pipe  were  placed  in  the  path  of 
the  gases  from  the  down-take  and  an  average  tempera- 
ture of  130°  F.  was  maintained.  Just  before  charging 
the  furnace  the  temperature  would  reach  150°  to  160°, 
while  shortly  afterward  the  temperature  would  drop  to 
100°.  The  pre-heated  blast  is  of  importance  in  promot- 
ing speed  in  the  furnace ;  but,  from  my  observations,  the 
cold  blast  gives  a  higher  rate  of  concentration.  Too 
great  speed  may  obviously  cause  low  concentration,  from 
the  fact  that  it  requires  a  certain  length  of  time  to  oxidize 
the  sulphides ;  and,  with  a  heavier  blast  to  promote  speed, 
the  result  is  a  hotter  top  and  a  low  ore-column,  since  the 
sulphides  will  melt  and  pass  to  the  crucible  before  they 
have  had  time  sufficient  to  be  acted  .  n  by  the  blast.  More- 
over, the  regulation  end  control  of  the  furnace  is  ren- 
dered easier  when  a  heated  blast  is  used.  Irregularities 
of  feeding  or  of  charged  material  do  not  affect  its  capac- 
ity or  its  equilibrium  so  easily  as  with  cold-blast  practice, 

249 


PYRITE  SMELTING. 

and  slag  of  a  higher  silica  content  can  be  made  and 
handled  with  greater  ease. 

The  minimum  of  fuel  depends  on  several  factors ; 
among  these,  cost,  quality  and  speed  of  furnace  come 
first.  At  the  plant  referred  to  we  used  8%  of  the  ore  on 
the  first  run,  speed  being  a  more  important  requisite  than 
high  concentration.  For  concentration  of  the  matte  2.5 
to  $%  of  coke  was  used,  except  for  the  first  10  or  15 
charges,  when  no  fuel  at  all  was  used,  as  the  heat  from  the 
first  run  kept  things  good  and  hot  for  some  time.  By 
using  but  2.5%  fuel  and  a  large  amount  of  silicious  ore  it 
gave  us  a  relatively  slow-driving  charge,  and  also  allowed 
of  a  concentration  of  3  into  I ;  whereas  with  5%  coke  the 
concentration  would  be  about  3  into  2,  and  sometimes 
even  less,  the  matte  merely  melting  and  running  through. 
This  first  matte  averaged  &%  copper. 

Much  also  depends  on  the  care  used  by  the  crew  below 
as  to  how  the  furnace  will  work  on  a  concentration  run. 
If  the  jacket-water  is  discharged  at  the  boiling  point,  all 
the  time,  the  furnace  will  act  much  better,  do  better  all 
round  work  and  be  far  easier  to  handle. 

Blast  pressure  depends  altogether  on  conditions  pre- 
vailing at  the  time.  Here,  with  rather  fine  charge  and 
an  ore-column  of  8  ft.,  we  used  a  pressure  of  24  oz. 
This  gives  a  hot  top  and  causes  much  flue-dust  to  be  car- 
ried over.  Of  the  latter  about  4^2  tons  were  made  each 
24  hours,  and  the  gold  and  silver  contents  were  highest 
near  the  furnace,  and  lowest  at  the  stack,  100  ft.  from 
the  down-take.  None  of  the  fume  was  ever  collected,  as 
no  means  were  at  hand  to  do  this. 

The  loss  of  sulphur  from  the  charge  averaged  75  %. 
The  furnace  at  this  plant  is  36  by  106  in.,  with  a  continu- 
ous-flow, blast-trapping  spout.  With  a  fairly  fine  charge 
and  blast  pressure  as  given,  it  would  smelt  140  tons  of 
charge  per  day,  and  could  have  handled  20  tons  more  if 
adequate  settling  arrangements  had  been  furnished. 

250 


P.  I.  MARSTON. 

Slags  could  not  be  settled  clean  if  the  forehearth  was 
crowded  too  fast. 

The  ordinary  blast-trapping  spout  for  continuous  slag 
flow,  such  as  was  used  here,  is,  generally  speaking,  a 
troublesome  device  and  requires  too  much  care  and  atten- 
tion. A  plain  tap-jacket,  of  good  design  and  construc- 
tion, will  do  better  work  and  give  better  satisfaction  in  the 
long  run. 

The  ore  charge  as  given  to  the  furnace  would  average 
o.&%  Cu,  and  this  would  give  clean  slags  when  the  speed 
of  the  furnace  was  kept  down  to  reasonable  limits.  A 
slag  of  high-silica  content  would  clean  better  than  one  of 
high-iron  content,  under  the  same  conditions  of  charge, 
blast  pressure,  speed,  etc.  With  0.5%  Cu  on  the  charge, 
clean  slags  can  be  made,  unless  much  zinc  be  present. 
With  a  high-zinc  slag  to  be  made,  the  copper  on  the 
charge  should  be  much  higher;  3%  at  least,  and  5%  is 
even  better.  The  concentration  made  here  on  the  first  run 
was  7  or  8  to  i;  and,  as  I  have  stated,  the  concentration 
of  the  first  matte,  3  to  I.  Any  ores  are  suitable  for 
pyritic  or  semi-pyritic  work,  except  those  the  lead  content 
of  which  is  above  5%.  As  low  as  i$%  of  FeS2  or  its 
equivalent  can  be  used  to  good  advantage  in  this  process ; 
but  it  is  better  to  use  25%  if  the  full  effect  is  to  be  de- 
rived from  the  burning  of  the  iron  and  sulphur.  Where  a 
slag  high  in  iron  is  made,  a  moderate  amount  of  zinc  has 
but  little,  if  any,  effect  on  the  fluidity  of  the  slag  or  its 
driving  qualities,  unless  much  alumina  is  present.  Con- 
siderable of  the  zinc  is  volatilized,  practically  all  of  the 
lead,  too,  and  this  phase  causes  loss  of  both  gold  and  sil- 
ver; the  loss  is  greater  in  the  case  of  silver,  however. 
The  slag  made  at  the  Ouray  plant  averaged  as  follows: 
FeO,  25.1;  CaO,  15.2;  BaO,  3.1;  ZnO,  5.0;  SiO2,  45.1; 
MgO,Al2O3  and  alkalies  to  100%.  The  average  values 
in  the  slags  were:  Au,  0.13  oz. ;  Ag,  1.6  oz. ;  Cu  always 
less  than  0.1%.  These  losses,  with  proper  facilities  for 
settling,  would  be  reduced  by  half. 

251 


PYRITE  SMELTING. 

Dr.  Carpenter  has  spoken  of  the  apparently  automatic 
action  of  the  furnace,  under  certain  conditions.  A  good 
example  of  this  selecting  process  came  to  my  notice  here. 
Our  iron  sulphide  was  of  poor  quality  and  variable ;  one 
noticeably  poor  lot  was  put  on  without  my  being  able  to 
sample  it.  At  2  A.  M.  the  furnace  stopped  making  matte, 
and  none  was  made  for  eight  hours,  although  it  had  been 
making  800  Ib.  per  hour,  and  did  so  again  as  soon 
as  it  regained  its  normal  condition.  An  analysis  of  the 
slag,  made  during  this  interruption,  gave:  FeO,  19.4; 
MnO,  0.9;  CaO,  12.1;  Zno,  5.8;  SiO2,  56.2;  A12O3,  1.4. 
All  the  iron  in  the  charge  was  used  for  the  slag,  leaving 
none  for  the  matte.  The  assay  of  this  slag  showed  retained 
values  as  follows:  Au,  0.008  oz.;  Ag.  1.8  oz. ;  Cu,  trace. 

•  P.  L.  MARSTON. 
Ouray,  Colo.,  May  24,  1905. 


252 


CONTRIBUTION  FROM  J.  PARKE  CHANNING. 

The  Editor: 

I  realize  that  it  is  impossible  ever  to  be  able  to  say  the 
last  word  on  any  technical  subject,  and  this  must  be  par- 
ticularly so  in  regard  to  metallurgical  operations.  At  the 
works  of  the  Tennessee  Copper  Company  we  have  made 
many  experiments,  and  have  much  improved  our  practice 
in  pyrite  smelting,  but  we  expect  to  do  better  still.  Not 
until  our  enlarged  plant  is  completed  do  we  hope  to  get 
the  full  benefits  of  pyrite  smelting,  and,  therefore,  all  that 
I  can  do  for  the  profession  is  to  report  progress. 

The  month  of  May  gave  us  the  best  results  which  we 
have  attained  since  our  change,  but  we  still  can  see  many 
points  in  which  improvement  is  sure  to  come ;  in  other 
words,  we  look  forward  to  a  somewhat  ideal  condition 
in  which,  instead  of  every  kind  of  accident  or  setback 
every  month,  we  will  have  only  one  kind  each  month.  In 
May  we  smelted  about  19,000  tons  of  ore  in  our  three  fur- 
naces, together  with  1,000  tons  of  custom  matte.  Includ- 
ing converter-slag  and  blast-furnace  products  and  first 
matte  re-smelted,  we  handled  a  little  over  30,000  tons  of 
material  per  month,  not  including  coke.  The  total  coke 
burned  for  this  30,000  tons  of  material  was  about  1,500 
tons,  which  is  considerably  higher  than  we  should  con- 
sume, partially  on  account  of  using  some  fine  material 
from  coke  stock,  and  also  on  account  of  the  extra  coke 
used  in  smelting  off  crusts. 

Permit  me  to  re-state  briefly  the  principal  features  of 
the  present  Tennessee  plant.  It  consist  of  three  blast- 
furnaces, each  56  by  180  in.  at  tuyeres,  the  total  height 
from  tuyere  to  feed-floor  being  18  ft.  Of  this,  14  feet 

253 


PYRITE    SMELTING. 

are  available  for  depth  of  charge,  the  top  4  feet  being  sim- 
ply added  so  as  to  get  proper  distribution  of  the  charge. 
Each  furnace  has  26  four-inch  tuyeres,  and  the  blast  is 
furnished  from  piston-blowing  engines.  This  blast-fur- 
nace is  exactly  the  same  one  that  was  formerly  used  for 
smelting  roasted  ore,  and  we  have  not  found  the  necessity 
of  any  marked  change  in  pynte  smelting.  Perhaps,  here 
may  be  a  good  place  to  mention  that  the  only  change 
which  it  was  found  necessary  to  make  in  the  furnace  was 
the  elimination  of  the  old  Boston  and  Montana  type  of 
cast-iron,  brick-lined  crucible,  and  its  replacement  by 
water  jackets  and  cast-iron  soleplate ;  so  that  the  present 
furnace  is  practically  water- jacketed  all  the  way  down. 

Two  furnaces  are  used  for  treating  ore  that  comes  from 
the  mines ;  the  third  furnace  concentrates  the  matte  from 
these  two  furnaces. 

The  Tennessee  Copper  Company  has  three  mines,  of 
which,  at  present,  only  two  are  being  wrought — the  Burra 
Burra  and  the  London.  The  Polk  County  mine  will  not 
be  put  in  commission  again  until  the  beginning  of  next 
year,  when  the  enlarged  plant  will  be  in  operation. 

The  ore  is  a  massive  sulphide,  consisting  of  nearly 
equal  parts  of  pyrite  and  pyrrhotite,  together  with  a  cer- 
tain proportion  of  chalcopyrite  and  silicious  minerals. 
Below  are  approximate  analyses  of  the  Burra  Burra 
and  London  ores : 

Burra  Burra.  London. 

Copper   2.2%  3.0% 


Sulphur    30.0 ' 

Iron     37.5 

Zinc    2.0 ' 

Lime  6.2 ' 

Magnesia    1.9' 

Alumina    3.9 ' 

Silica    10.3  ' 


21.0 
31.0 
0.8 
6.1 
2.5 
4.4 
26.3 


The  ore,  as  it  comes  from  the  mine,  is  crushed  coarsely, 
so  that  the  maximum  size  does  not  exceed  six  inches.  It 
is  then  sent  to  the  smelter  bins,  where  it  is  fed  into  the 
charge-cars.  The  ore  from  each  mine  is  kept  separate  on 

254 


/.  PARKE  CHANNING. 

account  of  the  difference  in  silica  content,  the  ordinary 
charges  being  as  follows : 

Burra   Burra.  London. 

Ore    4,000  Ib.  5,000  Ib. 

Quartz     1,000  "  400  " 

Coke   120  "  150  " 

These  proportions  are  not  always  adhered  to,  the 
amount  of  quartz  and  the  amount  of  coke  being  varied 
to  suit  conditions  of  the  furnace  and  the  grade  of  the 
matte.  In  loading  the  charge-cars,  the  sulphide  ore  is 
placed  underneath  the  quartz;  a  train  generally  consists 
of  four  cars  of  ore  charge  and  one  car  containing  either 
480  or  600  Ib.  coke.  The  coke  is  not  dumped  into  the 
furnace,  but  is  thrown  on  the  opposite  side  of  the  track 
upon  the  feed-floor.  The  charge-cars  dump  into  the  fur- 
nace, two  on  each  side.  Practice  at  our  plant  (like  that 
at  Mt.  Lyell)  shows  that  it  is  advisable  to  get  the  quartz 
near  the  center  of  the  furnace,  and  this  is  best  accom- 
plished by  putting  it  on  top  of  the  ore  charge.  On  the 
contrary,  it  is  found  advisable  to  keep  the  coke  as  near  the 
edges  and  corners  of  the  furnace  as  possible,  and  it  is 
fed  by  hand.  As  far  as  we  are  able  to  judge,  in  our 
charge  the  coke  performs  no  distinct  metallurgical  func- 
tion, but  seems  a  necessary  evil  which  must  be  endured  in 
order  to  prevent  crusts  adhering  to  the  jackets.  This 
crusting  of  the  furnace  is  the  bete  noir  of  pyrite  smelting, 
and  it  is  only  by  careful  manipulation  that  it  can  be 
avoided.  The  furnace  must  be  carefully  watched,  and, 
on  the  first  sign  of  approaching  crust,  either  it  is  re- 
moved with  long  bars,  or  else  large  chunks  of  sulphide 
ore  are  thrown  against  this  crust  to  prevent  its  increasing 
in  size. 

If  the  coke  is  dumped  into  the  furnace  and  not  fed 
against  the  jackets,  it  will  also  tend  toward  increasing 
the  crust.  We  have  found  repeatedly  that  a  one-night's 
Tun  (where  the  furnace  crew  was  short  and  the  coke 
could  not  be  properly  shoveled  in)  would  suffice  to  crust 
the  furnace  so  badly  that  it  would  take  three  dr  four 

255 


PYRITE    SMELTING. 

days  of  careful  manipulation  to  bring  it  around  into  good 
shape.  We  had  a  great  deal  of  trouble  in  this  respect 
during  the  last  six  months,  not  only  on  account  of  short- 
age of  labor,  but  also  by  reason  of  the  fact  that  we  lost 
the  use  of  the  'loop'  track  around  the  furnaces  during 
the  enlargement  of  the  smelter  building. 

In  the  old  days  of  roasted-ore  smelting,  the  average 
depth  of  charge  above  the  tuyeres  was  probably  not 
more  than  8  or  9  feet.  In  pyrite  smelting,  if  the  furnace 
is  running  well,  the  depth  of  charge  will  vary  from  12  to 
IJ.  ft,  and  under  these  conditions  the  furnace  runs  better 
and  gives  a  better  elimination  of  sulphur  than  with  a 
less  depth  of  charge. 

Under  normal  conditions,  a  furnace  will  treat  375  tons 
of  sulphide  ore  per  day,  and,  at  that  rate,  should  be  in 
action  about  27  days  per  month;  that  is,  each  furnace 
may  be  expected  to  be  down  for  one  week  every  two 
months,  thus  giving  the  average  ore  per  furnace  per 
month  of  about  10,000  tons.  I  believe  in  time  we  shall 
be  able  to  exceed  this,  as  we  have  frequently  put  through 
over  400  tons  in  24  hours,  not  including  quartz  flux. 

When  running*  at  this  rate  of  375  tons  (per  day  of  24 
hours)  our  engines  will  make  about  68  to  75  rev.  per 
min.,  or  an  average  of  about  17,000  cu.  ft.  of  free  air 
per  minute.  These  figures  are  accurate  and  allow  for 
losses  due  to  slip  or  leakage.  These  figures  will  be  par- 
ticularly interesting,  as  we  can  determine  the  slip  and 
leakage  with  our  piston  blower — a  correction  rather  diffi- 
cult to  make  with  a  rotary  blower.  This  volume  of  air 
is  not  much  different  from  the  amount  used  when  we 
were  smelting  roasted  ore,  only  under  former  conditions 
the  furnace  would  put  through  a  larger  tonnage.  We 
have  repeatedly  tried  using  a  larger  volume  of  blast  on 
the  furnace,  but  not  with  great  success,  the  tendency 
being  to  crust  the  furnace.  What  we  may  do  in  the 
future  is  hard  to  tell. 

The  furnace  is  arranged  as  usual,  with  a  continuous 

256 


J.  PARKE  CHANN1NG. 

overflow,  the  resulting  matte  and  slag  going  into  a  16- 
ft.  circular  'settler/  which  we  now  line  with  chrome 
brick.  The  slag  overflows  into  cars  and  is  carried  to  the 
dump.  The  first  matte  is  intermittently  tapped  into 
other  slag-cars,  moved  to  a  slightly  inclined  yard  in  front 
of  the  furnace  building  and  there  poured  into  flue-dust 
beds.  After  it  has  solidified  and  cooled,  it  is  broken  by 
hand  (as  near  6-in.  pieces  as  possible),  loaded  into  rail- 
road-cars and  brought  up  to  the  smelter-bins. 

The  second  operation  consists  in  smelting  this  matte, 
together  with  quartz,  converter-slag  and  blast-furnace 
cleaning,  so  as  to  produce  a  matte  of  a  grade  sufficiently 
high  to  convert.  The  same  kind  of  furnace  is  used  for 
this  second  operation,  but  the  furnace  is  changed  occa- 
sionally, as  it  is  found  that  a  matte-charge  will  clean  out 
a  crusted  ore-furnace,  and  conversely  an  ore-charge  will 
clear  out  a  crusted  matte-furnace. 

The  matte-concentrating  furnace  does  not  run  as  rap- 
idly as  the  green-ore  furnace,  the  tonnage  per  week  vary- 
ing from  800  to  1,300  ton  of  matte,  depending  a  great  deal 
upon  the  grade  of  the  matte  and  the  condition  of  the 
furnace.  In  the  early  days  of  our  pyrite  smelting  we 
found  no  great  difficulty  in  running  an  old-type  furnace 
or;  a  green-ore  charge;  but,  whenever  we  attempted  a 
concentration  charge,  in  less  than  24  hours  the  crucible 
became  so  hot  that  it  leaked  in  every  direction,  and  it 
became  impossible  to  keep  the  matte  in  it.  One  by  one 
the  crucibles  were  changed  by  the  substitution  of  'baby 
jackets/  the  first  furnace  adapted  being  put  on  concen- 
tration charge  (such  as  I  will  show  herewith),  running 
from  December  9  to  15,  1904.  I  also  give  the  average 
of  the  matte  produced  on  the  first  and  second  operation, 
respectively,  during  the  month  of  May,  that  on  the  first 
operation  being  about  12%  and  that  on  the  second  about 
43%.  This  grade  of  matte  on  the  second  operation 
is  somewhat  complicated  by  the  addition  to  this  charge 
of  45%  custom  matte,  which  is  simply  re-melted  in.  this 

257 


PYRITE  SMELTING. 

furnace,  and  then  converted.  It  tends  to  mask  the  real 
operation,  though  we  assume  that  it  has  no  particular 
effect  upon  the  concentration. 

MATTE  ANALYSES. 

First.  Second. 

Copper   11.9%  42.8% 

Sulphur     25.6  "  24.6  " 

Iron 54.0  "  29.2  " 

Zinc 1.7  "  1.0 " 

It  will  be  remembered  that  the  slag  which  we  pro- 
duced in  ordinary  roasted-ore  smelting  ran  about  33%  to 
35%  silica.  It  is  not  yet  found  possible  to  do  this  in 
p>  rite  smelting.  The  fact  seems  to  be,  as  has  been  before 
stated,  that,  with  a  given  ore  and  a  given  furnace,  the 
combination  makes  its  own  type  of  slag,  from  which  it 
is  impossible  to  make  any  radical  changes.  Therefore 
we  have,  so  far,  arrived  at  the  fact  that  the  slag  at  our 
first  operation  will  run  about  40%  silica.  It  makes  no 
difference  whether  we  increase,  or  diminish,  the  amount 
of  quartz  on  the  charge;  the  slag  will  remain  at  about 
40%  silica,  and  the  only  change  will  be  an  increase,  or 
decrease,  in  the  grade  of  the  matte.  In  fact,  the  method 
of  running  the  furnace  is  to  vary  the  quartz  charge  so  as 
to  keep  a  constant  grade  of  matte.  This  grade  varies 
from  9%  to  16%,  and,  under  present  conditions,  we  con- 
sider a  12%  matte  the  most  economical.  While  making 
this  grade  of  matte,  the  slag  will  run  from  0.18%  to 
0.27%  copper.  Herewith  I  give  analyses  of  our  slag  on 
both  the  first  and  second  operations: 

SLAG  ANALYSES. 

First.  Second. 

Copper   0.2%  0.6% 

Sulphur     0.7 "  1.3 

Iron  oxide   42.5  "  52.6 

Zinc  oxide    1.5 "  1.1 

Lime 7.5  "  2.6  ' 

Magnesia    2.0 "  0.7 

Alumina    5.5  "  4.2 

Silica    40.0 "  36.5 

It  will  be  observed,  from  these  analyses,  that,  on  the 
first  operation,  we  make  about  a  'quarter '  slag,  the  factor 

258 


/.  PARKE  CHANNING. 

of  which  is  0.29.  We  notice,  however,  that  the  silica 
is  much  higher  than  the  ordinary  'quarter'  slag  such  as 
a  lead  furnace  will  make ;  but,  as  I  have  said  before,  it  is 
absolutely  impossible  for  us  to  keep  this  silica  down.  I 
have  no  doubt  that  it  is  because  of  this  'quarter'  slag  that 
our  copper  runs  so  low  on  the  first  operation.  A  straight 
charge  of  Burra  Burra  ore  will  give  a  better  ratio  than  a 
London  charge,  or  even  a  mixture  of  the  two.  We  did 
make  an  experimental  run  for  about  two  days,  adding 
some  barren  limestone  to  the  charge  so  as  to  make  the 
formula  an  exact  'quarter'  slag,  but  the  campaign  was  so 
short  that  we  were  not  able  to  see  any  improvement  in  the 
slag-losses. 

In  the  first  concentration,  carried  out  in  December, 
1904,  we  took  low-grade  matte  from  our  first  green-ore 
smelting,  which  probably  did  not  run  higher  than  9% 
copper,  and  in  one  operation  brought  it  up  to  50%. 
Under  these  conditions  we  made  practically  an  iron-silica 
slag,  with  a  specific  gravity  of  about  3.8.  Under  these 
conditions  the  slag  ran  high  in  copper.  The  results  of 
runs  for  two  different  weeks  in  December,  1904,  are  given 
herewith,  simply  to  show  what  can  be  expected  with  con- 
centration of  this  kind.  In  this  operation  we  found  no 
difficulty  in  making  matte  of  any  grade  desired,  simply  by 
varying  the  amount  of  quartz ;  and,  as  we  had  a  large  ac- 
cumulation of  low-grade  matte,  we  thought  it  better  pol- 
icy to  concentrate  highly  so  as  to  get  a  maximum  output 
from  the  converters.  We  soon  found  that  these  concen- 
tration losses  could  be  reduced  by  adding  a  certain  amount 
of  sulphide  ore  to  the  charge.  This  not  only  decreased 
the  rate  of  concentration,  but  also  improved  the  composi- 
tion of  the  slag  by  adding  to  it  a  certain  proportion  of 
other  bases.  This  improvement  in  composition  can  be 
seen  by  looking  at  the  complete  analyses  of  slag,  as 
herewith. 

For  comparison,  I  give  the  results  of  three  different 
week-runs  on  concentration,  the  first  two  being  straight, 

259 


PYRITE    SMELTING. 

and  the  last  one  showing,  about  the  type  which  we  now 
follow : 

TYPICAL.  CONCENTRATION  RUNS. 

Dec.  9  to  15.  .Dec.  16  to  22.  Jan.  2  to  8. 

1904.  1904.  1905. 

Tons.  Tons.  Tons. 

Sulphide  ore ....  279 

Converter  slag 130  210  162 

Blast-furnace    slag ....  320 

Quartz  flux    562  527  307 

Custom  matte,  45% 252 

First  matte,  10%  to  12%..     1,296  1,285  808 

Total     1,988  2,022  2,118 

Tons.  Tons.  Tons. 

Coke   used    89                      71  151 

Coke  percentage    4.5                      3.5  7.1 

Slag  Analyses: 

Copper 1.01%  1.03%  0.65% 

Iron  oxide   58.6%  58.4%  54.2% 

Silica    33.9%  34.2%  38.8% 

Matte    Produced: 

Copper   48.2%  52.5%  44.2% 

We  still  have  on  hand  an  accumulation  of  custom  matte, 
which  we  are  trying  to  clean  up ;  and,  as  soon  as  this  is 
out  of  the  way,  it  is  our  intention  to  add  barren  limestone 
to  this  concentration  charge  so  as  to  make  a  'quarter'  slag 
and  determine,  experimentally,  whether  we  can  concen- 
trate a  13%  matte  to  a  40%  matte  with  comparatively  low 
slag-losses.  As  far  as  I  am  aware,  this  particular  kind  of 
work  has  not  been  carried  out  anywhere  else  in  the  United 
States,  and  it  will  be  interesting  to  see  what  results  are 
achieved.  In  certain  of  the  Salt  Lake  valley  smelters  a 
concentration  of  low-grade  matte  is  made  in  which  the 
silicious  material  added  is  usually  an  ore  containing  more 
or  less  iron,  and  also  considerable  fine ;  and,  as  a  rule,  to 
this  charge  some  limestone  is  added.  Under  these  condi- 
tions it  is  difficult  to  get  more  than  a  concentration  of  3 
into  2,  or  2  into  I,  at  the  utmost.  I  am  not  prepared  to 
say  whether  in  our  case  there  would  be  any  commercial 
gain  in  adding  limestone,  as  unquestionably  more  quartz 
we'ild  have  to  be  used ;  and,  as  both  quartz  and  lime  cost 
money  and  it  takes  money  to  smelt  them,  it  is  a  question 
of  balancing  the  copper  saving  as  against  the  added  cost 

260 


7.  PARKE  CHANNING. 

of  the  flux.  As  I  have  before  stated,  mechanical  difficul- 
ties (due  to  the  inexperience  of  our  men  and  also  to  the 
interference  incidental  to  the  enlargement  of  our  plant) 
have,  to  a  large  degree,  made  our  operation  irregular. 

I  give  herewith  the  results  on  a  fairly  average  week's 
run  in  which  two  furnaces  were  smelting  straight  sulphide 
ore  and  the  third  furnace  was  treating  matte  (from  the 
first  operation  and  also  custom  matte).  The  amount  of 
matte  concentrated  was  not  equal  to  that  produced  in  the 
first  operation.  The  figures  are  only  given  to  show  about 
how  the  furnace  tonnage  ran.  The  plant,  as  at  present 
constituted,  is  not  properly  balanced,  and  it  is  our  inten- 
tion, when  more  furnaces  are  available,  to  treat  the  con- 
verter-slag with  the  green  ore,  so  as  to  reduce  its  copper 
content  as  much  as  possible.  Under  present  conditions 
it  is  treated  in  the  concentration  furnace,  and  so,  when 
finally  discharged,  it  carries  at  least  0.6%  copper. 


WEEKLY    TONNAGE. 


No.  1. 


Tons. 
Furnace. 

Sulphide   ore    2,667 

Converter   slag    

Quartz  flux    559 

Custom  matte,  45% 

First  matte,  12%. 


Total  charge 3,226 


Coke  used    

Coke  percentage   % 

Tons  of  charge  per  day.  .. 


Tons. 

92 

2.9 

461 


No.  2. 

No.  3. 

Total 

Tons. 

Tons. 

Tons. 

2,540 

253 

5,460 

721 

721 

'456 

220 

1,235 

231 

231 

"20 

557 

577 

3,016 

Tons. 

99 

3.3 

431 


1,982 

Tons. 

174 

8.8 

283 


8,224 

Tons. 
365 
4.4 


It  is  almost  unnecessary  to  state,  that  in  all  of  our  work, 
we  have  used  nothing  but  cold  blast ;  and,  thus  far,  the 
use  of  hot  blast  in  treating  a  heavy  sulphide  ore  like  ours 
has  not,  as  far  as  I  can  see,  been  of  any  advantage.  At 
Mt.Lyell  it  was  formerly  supposed  that  it  was  necessary; 
but,  after  four  years'  practice,  the  use  of  it  has  been  finally 
abandoned.  At  the  plant  of  our  neighbors,  the  Ducktown 
Sulphur,  Copper  &  Iron  Company,  Mr.  Freeland  put  in  a 

261 


PYRITE  SMELTING. 

U-pipe  hot-blast  stove,  but  could  find  no  improvement 
either  metallurgically  or  commercially  therefrom,  either 
on  roasted  or  unroasted  ore.  He,  therefore,  for  the  pres- 
ent has  abandoned  any  further  attempt  to  utilize  hot  blast. 

In  The  Engineering  and  Mining  Journal,  June  8,  1905, 
in  two  references  to  hot  blast,  both  of  them  seem  to 
agree  that  cold  blast  is  an  aid  to  concentration.  The  fact 
is,  my  colleagues  and  I  believe  the  time  is  not  distant 
when  we,  perhaps,  will  be  able  to  make  from  our  ore,  in 
one  operation,  a  matte  that  can  be  directly  converted.  At 
the  Ducktown  Sulphur,  Copper  &  Iron  Company's  plant 
the  furnaces  have  occasionally  produced  high-grade  matte 
for  24  hours  at  a  time;  yet,  so  far,  they  have  not  been 
able  to  keep  up  this  concentration  and  at  the  same  time 
maintain  the  capacity  of  the  furnaces. 

The  accompanying  table,  showing  the  composition  of 
our  matte,  may  prove  interesting,  particularly  as  it  shows 
that  the  amount  of  sulphur  present  is  considerably  less 
than  that  which  would  be  expected  (from  an  accepted 
formula  for  matte,  Cu2S.FeS).  For  a  time  we  thought 
that  we  had  an  excess  of  iron  in  our  matte,  but  we  finally 
found  that  the  actual  iron  very  nearly  agreed  with  the 
theoretical,  the  only  difference  being  that  a  certain  amount 
of  the  sulphur  was  replaced  by  oxygen,  presumably  part 
of  the  iron  being  FeS  and  the  other  part  Fe3O4. 

We  hope  that  the  time  will  come  when  the  barring  of 
furnaces  will  be  reduced  to  a  minimum.  At  present,  if 
a  furnace  gets  in  such  bad  shape  as  to  be  pretty  well 
crusted  on  top,  we  allow  the  furnace  to  run  down,  adding 
several  charges  of  slag,  and  coke.  The  blowing  engine  is 
then  reduced  in  speed,  so  that  it  delivers  very  little  air 
to  the  furnace,  and  long  il/2  in.  steel  bars,  with  chisel- 
shaped  ends,  made  of  2  by  4-in.  steel,  are  driven  down 
behind  the  crusts.  A  chain  is  slipped  over  the  bar  and 
attached  to  one  of  the  electric  locomotives,  which  slowly 
pulls  it  and  the  crusts  over  into  the  furnace.  This  is 
a  vast  improvement  on  the  former  method  of  attempt- 

262 


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PYRITE    SMELTING. 

ing  to  attack  these  crusts  with  small  bars  and  by  hand 
alone. 

The  addition  to  the  blast-furnace  plant  will  consist  of 
four  furnaces,  56  by  270  in.  at  the  tuyeres,  but  of  the 
same  height  and  general  shape  as  the  old  furnaces,  except- 
ing that  the  lower  jackets  will  be  carried  down  to  the 
sole-plate.  These  furnaces  will  have  rounded  corners, 
so  as  to  facilitate  barring,  and  the  number  of  tuyeres  will 
be  increased  to  26  on  the  rear  side  of  the  furnace  and  24 
on  the  front  side,  each  tuyere  being  of  about  3-in.  diam- 
eter. We  are  of  the  opinion  that  a  large  number  of  tuy- 
eres, more  closely  spaced,  will  give  us  better  results.  In 
other  words,  each  tuyere  is  a  nucleus  of  activity';  so 
that,  if  carried  to  its  logical  extreme,  a  narrow  slot 
would  be  the  ideal  opening  for  the  air  blast.  This,  of 
course,  is  an  impossible  construction.  The  tops  of  the 
furnaces  will  be  so  modified  that  in  case  it  becomes 
necessary  to  do  any  heavy  barring,  extra  doors  above  the 
feed-doors  will  be  thrown  open  and  bars  held  vertically 
will  be  driven  by  men  on  a  platform  above  the  feed- 
floor.  Each  furnace  will  be  supplied  with  air  by  a  hori- 
zontal-piston blowing  engine,  capable  of  delivering3O,ooo 
cu.  ft.  free  air  per  minute.  Only  three  of  these  new  en- 
gines will  be  provided,  as  it  is  estimated  that  in  the  final 
plant,  which  will  consist  of  seven  furnaces  and  six  blow- 
ing engines,  one  furnace  will  always  be  out  of  blast. 

It  is  still  a  little  too  early  to  determine  exactly  what  the 
commercial  saving  will  be  on  pyrite  smetling.  We  have 
certainly  eliminated  the  roast-yard  expense,  which 
amounts  to  400.  per  ton.  I  believe  that  the  blast-furnace 
expense  per  ton  of  green'ore  will  be  about  the  same ;  and 
I  am  of  the  opinion  that  we  will  save  at  least  four  pounds 
more  of  copper  than  we  did  in  the  old  method.  In  addi- 
tion to  this,  much  to  our  gratification,  we  have  found  that 
the  gases  from  the  furnace  are  so  rich  in  SO2  that  we  can 
make  acid  from  them  by  the  chamber  process.  This  will 
give  us  a  by-product,  which  will  be  of  great  value  in  the 

264 


/.  PARKE  CHANNING. 

South  for  the  purpose  of  making  fertilizers,  and  not  only 
will  it  operate  toward  reducing  the  volume  of  gases  given 
to  the  atmosphere,  but  will  prove  a  source  of  considerable 
revenue.  We  are,  however,  providing  the  new  plant  with 
a  stack  325  ft.  high  (internal  diameter  20  ft.),  so  as  to 
give  us  perfect  draught,  which  is  desirable  in  pyrite  smelt- 
ing, as  without  proper  draught,  and  with  gases  leaking 
from  the  doors,  the  feed-flo'or  is  by  no  means  a  comfort- 
able place. 

I  regret  that  I  am  not  in  a  position  to  say  that  we  have 
absolutely  settled  everything  to  our  satisfaction.  Perhaps 
it  is  well  that  such  is  the  case,  for  all  industries  either 
advance  or  recede ;  they  never  stand  still. 

J.  PARKE  CHANNING. 
New  York,  June  12,  1905. 


265 


RATIO    OF    HEARTH    AREA    TO    FURNACE 
CAPACITY.1 

BY  W.   RANDOLPH  VAN  LJEW. 

It  would  be  a  matter  of  great  value  to  metallurgical 
practice  if,  instead  of  each  manager,  or  superintendent, 
having  his  own  particular  notion  as  to  the  width  to  be 
given  a  blast  furnace,  it  could  be  determined  on  a  scien- 
tific basis  what  should  be  the  width  best  adapted  to 
secure  the  most  economical  costs,  and  the  largest  ton- 
nage smelted,  per  square  foot  of  hearth  area  at  the 
tuyeres. 

I  say  tonnage  smelted  per  square  foot  of  hearth  area 
at  the  tuyeres,  as  it  is  the  only  true  standard  by  which 
to  gauge,  or  compare,  the  workings  of  different  types 
of  furnaces.  A  furnace  15  ft.  long,  smelting  500  tons  of 
material  a  day,  could  just  as  well  be  made  150  ft.  long, 
and  to  smelt  5,000  tons  per  day.  It  is  simply  a  ques- 
tion of  spouts  and  settlers  at  regular  intervals.  Two 
furnaces  may  be  run  side  by  side,  one  smelting  700  tons, 
the  other  400  tons,  yet  the  latter  may  be  doing  half  as 
much  more  work,  as  it  all  depends  on  the  number  of 
square  feet  of  area  available  for  smelting  at  the  tuyere 
zone. 

Until  recently,  very  little  has  been  published  concern- 
ing the  tonnage  treated  by  furnaces  of  different  sizes 
situated  in  different  localities.  This  has  made  it  diffi- 
cult for  those  either  contemplating  the  erection  of  plants 
or  the  modification  of  existing  furnaces,  to  form  an  idea 
of  what  the  different  types  of  furnaces  can  do  in  the  way 
of  capacity. 

This  spirit  of  secrecy,  in  the  end,  always  operates 
against  those  who  practise  it.  It  seems  to  have  charac- 

*The  Engineering  and  Mining  Journal,  March  21, 1903,  page  4:4.2. 

266 


W.  RANDOLPPI  VAN  HEW. 

terized  the  metallurgy  of  copper  more  than  that  of 
any  other  metal.  As  an  instance,  I  may  mention  the 
fire  refining  of  copper,  the  art  of  which,  until  the  past 
few  years,  was  jealously  guarded,  and  practically  handed 
down  from  father  to  son.  Again,  in  the  province  of  the 
electrolytic  refining  of  copper,  until  quite  lately,  the 
doors  were  closed  to  all,  and  this  spirit  even  survives 
to-day  in  some  Eastern  refineries,  in  spite  of  their 
general  operations,  currents  and  strength  of  electrolyte 
being,  within  narrow  limits,  known  to  most  of  the  pro- 
fession. 

As  an  illustration  of  the  extremes  to  which  this  spirit 
lends  itself,  it  is  but  necessary  to  point  to  our  English 
cousins,  in  the  metallurgy  of  iron,  where  this  same  nar- 
row spirit  is  exhibited,  each  company  wrapping  itself 
within  its  own  walls,  so  that  their  representatives,  com- 
ing to  this  country,  look  in  open-mouthed  astonish- 
ment at  the  way  in  which  the  doors  of  our  large  steel 
plants  are  thrown  open  to  them,  and  at  the  freedom 
with  which  our  methods  are  explained  to  them ;  this  very 
interchange  of  ideas,  and  improved  practice  among  our- 
selves, no  doubt  being  one  of  the  principal  factors  in 
placing  the  United  States  in  that  foremost  position 
which  she  holds  in  the  steel  industry  to-day. 

Fortunately,  those  engaged  in  the  metallurgy  of 
copper  are,  at  last,  following  in  the  footsteps  of  our 
friends,  the  iron  metallurgists.  Among  those  who  have 
taken  up  the  cudgel  in  this  respect  are  Mr.  William  A. 
Heywood,  of  the  Tennessee  Copper  Company,  and  Mr. 
Paul  Johnson,  of  the  Greenwood,  British  Columbia, 
Company,  who,  in  recent  issues  of  The  Engineering  and 
Mining  Journal,  have  given  interesting  data,  that  afford 
a  valuable  study  in  widths  of  furnaces  as  related  to  their 
output.  Why  cannot  each  superintending  metallurgist 
who  may  read  these  articles  contribute  his  quota  also  to 
the  fund  of  general  experience,  that,  from  the  whole,  we 
may  all  of  us  benefit,  and,  having  considered  the  differ- 

207 


PYR1TE    SMELTING. 

ence  in  different  ores,  decide,  within  approximate  limits, 
on  that  width  which  would  seem  to  give  the  best  re- 
sults ? 

As  I  have  said,  the  length  of  a  furnace  is  immaterial ; 
as  to  width,  the  narrowest  furnace,  of  the  usual  rect- 
angular type,  that  I  know  is  35  in.  wide  at  the  tuyeres ; 
the  widest  is  56  in.,  or  65  per  cent  wider.  It  was  my 
privilege,  while  in  charge  of  one  of  the  large  b-last-fur- 
nace  plants  in  Montana,  to  observe  the  workings  of 
furnaces  of  different  widths  on  the  same  ores,  the  one 
style  44  by  100  in.,  the  other  56  by  180  in.,  and  the 
result  from  every  standpoint  was  in  favor  of  the  nar- 
rower furnace. 

The  56-in.  furnace  was  much  higher  from  the  tuyeres 
to  the  charging  floor,  but  the  burden  on  the  tuyeres 
was  kept  as  nearly  as  possible  at  the  same  height. 

The  56-in.  furnace  was  fed  by  charging  cars,  the  44-in. 
by  charging  wheelbarrows,  dumped  directly  into  the  fur- 
nace. Slags  were  very  nearly  the  same,  2  to  3  per  cent 
more  iron  not  uncommonly  being  given  to  the  slags 
from  the  56-in.  furnace. 

The  slag  contents  in  copper  were  also  the  same,  and 
very  low.  The  44  by  100  in.  furnace  would  average, 
month  after  month,  215  tons  per  24  hours,  not  includ- 
ing coke. 

The  56  by  180  in.  furnaces,  at  two  different  Montana 
plants  smelting  Butte  ores,  smelted  400  to  500  tons  per 
day,  with  an  approximate  average  of  420  tons. 

The  44  by  100  in.  furnace  had  30.5  sq.  ft.  of  hearth 
area  at  the  tuyeres,  which  gives  7.06  tons  smelted  per 
square  foot  of  hearth. 

The  56  by  i8o-in.  furnace  had  70  sq.  ft.  of  area,  which 
gives  6.0  tons  smelted  per  square  foot  of  hearth. 

The  44-in.  furnace  required  19  oz.  blast,  the  56-in.  fur- 
nace required  27  oz.  blast  and  10  per  cent  more  total 
fuel  to  do  the  smelting,  the  slags  in  both  cases  running 
between  38  and  42  per  cent  silica,  18  and  21  per  cent 

268 


W.  RANDOLPH  VAN  LIEW. 

iron,  18  and  24  per  cent  lime,  and  0.2  to  0.4  per  cent 
copper. 

The  tonnage  of  a  furnace  is  affected  also  by  the 
amount  of  iron  in  the  slag;  up  to  a  certain  point  the 
more  iron  the  faster  the  furnace  will  smelt. 

Mr.  Heywood,  of  the  Tennessee  Copper  Company,  in 
his  interesting  and  valuable  article,  contained  in  the 
Journal?  states  that  on  Tennessee  ores,  which,  if  I  am 
correctly  informed,  carry  enough  iron  to  offer  the  de- 
sired quantity  for  good,  easy  running  slags,  the  average 
work  of  a  56  by  iSoin.  blast  furnace  was  495  tons  per 
day,  or  7.07  tons  smelted  per  square  foot  of  hearth. 
For  one  month  561  tons  were  smelted  per  day,  or  8.01 
tons  per  square  foot  of  hearth ;  for  seven  days  the  aver- 
age output  was  615  tons  per  day,  or  8.8  tons  per  square 
foot  of  hearth,  while  the  maximum  tonnage  for  any  one 
day  was  657  tons,  or  9.4  tons  smelted  per  square  foot 
of  hearth  area,  the  blast  pressure  varying  from  20  to 
40  oz.,  while  composition  of  the  slags  was  not  given. 

Turning  from  the  wide  56  and  44  in.  furnaces,  smelt- 
ing Tennessee  and  Montana  ores,  we  will  see,  by  refer- 
ring to  the  equally  valuable  article  by  Mr.  Paul  John- 
son, of  the  Greenwood  Smelter  in  British  Columbia,  in 
the  Journal,2  that  we  can  form  an  idea  of  the  work  of  a 
still  narrower  type  of  blast  furnace. 

The  furnaces  at  Greenwood  are  only  42  in.  wide. 
The  size  of  the  furnace  at  the  tuyeres  is  42  by  150  in., 
or  43.7  sq.  ft.  of  hearth  area.  The  daily  tonnage  of  ore 
is  given  as  380.5  tons,  or  8.7  tons  per  square  foot  of 
hearth  area.  The  highest  average  tonnage  treated 
during  one  month  was  428.6  tons  per  day,  or  9.8  tons 
per  square  foot  of  hearth,  and  the  highest  for  a  single 
day  was  460  tons  of  ore,  or  10.5  tons  per  square  foot  of 
hearth.  The  average  slags  are  stated  to  contain  39.8 
per  cent  silica,  23.6  per  cent  iron,  19.6  per  cent  lime  and 

*The  Engineering  and  Mining  Journal,  July  26,  1902,  page  119. 
'/dew,  Aug.  23,  1902.  page  251. 

209 


PYRITE    SMELTING. 

0.321  per  cent  copper,  when  producing  a  50.1  per  cent 
matte  and  using  a  blast  pressure  of  14.15  °z- 

We  come  now  to  a  still  narrower  type,  a  furnace  35 
in.  wide  at  the  tuyeres.  It  was  my  privilege  to  operate 
such  a  furnace  on  Old  Dominion  ores,  duplicating  all 
the  conditions  that  would  be  required  of  it  under  matte 
smelting  and  converter  practice.  The  trial  lasted  five 
days,  when  the  sulphides  in  the  bins  were  used  up  and 
the  furnace  returned  to  black  copper  smelting. 

The  results  are  of  interest  as  bearing  on  the  subject 
of  widths  of  furnaces.  The  furnace  in  question  was 
35  by  122  in.  at  the  tuyeres,  that  is,  it  had  29.68  sq.  ft. 
of  hearth  area.  Not  including  coke,  and  under  its 
duplicated  converter  conditions,  the  tonnage  was  as 
follows : 

Tons  per  sq.  ft. 

Total  tons,  of  hearth  area. 

First   day 255.0  8.60 

Second   day 282.0  9.50 

Third  day    283.8  9.56 

Fourth    day    322.0  10.84 

Fifth   day 334.0  11.25 

On  the  fourth  and  fifth  days  the  furnace  ran  on  7  per 
cent  coke,  and  was  running  faster,  when  changed  back 
to  black  copper  smelting,  than  two  days  before,  when 
placed  on  7  per  cent  fuel. 

The  slags  made  varied  between  37  and  41  per  cent 
silica,  25  and  29  per  cent  iron,  n  and  15  per  cent  lime, 
9  and  14  per  cent  alumina. 

The  slags  ran  from  0.20  to  0.30  per  cent  copper  for 
42  to  48  per  cent  matte ;  from  0.30  to  0.40  per  cent  cop- 
per for  48  to  53  per  cent  matte.  The  blast  was  kept  at 
21  oz. 

While  I  appreciate  that  a  campaign  of  five  days  does 
not  possess  the  same  value  a?  one  of  many  months,  still 
the  fact  remains  patent  that  even  so  short  a  trial  will 
possess  its  value,  as  indicating  the  possibilities  of  the 
narrow  type  of  furnace. 

Of  the  four  types  of  furnaces — the    56-in.  on  Ten- 

270 


W.  RANDOLPH  VAN  L1EW. 

nessee  ores,  the  56  and  44-in.  on  Butte  ores,  the  42-in. 
on  British  Columbia  ores,  and  the  35-in.  on  Old  Do- 
minion ores — the  advantage  seems  overwhelmingly  in 
favor  of  the  two  narrower  types  of  furnaces,  both  from 
the  standpoint  of  tonnage  smelted  per  square  foot  of 
hearth  area  at  the  tuyeres,  and  of  economy  of  power 
for  blast  pressure.  In  the  matter  of  feeding,  I  have 
found  but  little  difference  between  hand  feeding  and 
charging  direct  from  barrows — if  the  workmen  have 
been  trained  to  place  their  charges  where  needed;  but 
comparing  either  of  these  to  charging  by  cars,  my  own 
experience  duplicates  that  of  Mr.  Paul  Johnson.  While 
automatic  charging  from  cars  permits  larger  bin  ca- 
pacity, the  location  of  bins  farther  from  'the  furnace,  and 
a  certain  amount  of  labor  saved,  yet  it  can  be  used  only 
by  sacrificing  other  conditions,  the  maintenance  of 
which  to  the  metallurgist — and  to  the  company — are 
more  to  be  desired.  It  is  poor  metallurgical  practice 
to  use  any  manner  of  feeding  that  will  increase  the  fuel 
demanded,  and  also  choke  the  output  of  your  furnace. 
These  two  things  charging  by  cars  unquestionably  does, 
while  considering  the  extra  labor  involved  in  maintain- 
ing the  other  conditions  about  the  furnaces,  there  is  not 
so  much  labor  saved,  on  the  whole,  as  the  uninitiated 
believe.  Figuring  simply  the  labor  cost  per  ton  of  ore, 
the  advantage  will  be  in  favor  of  the  mechanical  feeding 
by  cars,  but  placing  against  this  saving  the  resultant 
interior  condition  of  furnace,  the  extra  coke,  and  the  de- 
creased tonnage  per  square  foot  of  hearth  area,  the 
smelting  costs  will  be  higher  with  the  car  charging. 

To  add  to  this  data,  it  would  be  of  much  value  and 
interest  to  the  profession  if  the  managers  or  superin- 
tendents of  smelting  plants,  possessing  the  40  and  5O-in. 
width  of  blast  furnace,  would  give  us  the  possibilities  of 
those  types. 


271 


CONTRIBUTION  BY  J.  PARKE  CHANNING. 

The  Editor: 

Sir — I  have  read  Mr.  Van  Liew's  communication  on 
this  subject,  in  your  issue  of  to-day,  and  quite  agree 
with  him  that  it  is  desirable  to  disseminate  as  much  as 
possible  all  information  concerning  metallurgical  prac- 
tice for  the  common  good  of  all  concerned. 

The  object  of  smelting  any  ore  is  to  secure  as  great 
an  extraction  as»  possible  at  a  minimum  cost.  In  other 
words,  the  cost  of  extraction  is  the  operating  expense, 
plus  the  value  of  the  slag  loss. 

Certainly,  Mr.  Van  Liew's  figures  seem  to  indicate 
that  a  narrow  furnace  gives  a  greater  tonnage  per 
square  foot  of  hearth  area ;  but  are  we  striving  for  this 
particular  record?  Is  it  not  rather  the  broad  question 
of  cheap  and  efficient  smelting? 

I  do  not  agree  with  Mr.  Van  Liew  that  a  furnace  150 
ft.  long  would  do  ten  times  as  much  work  as  one  15  ft. 
long.  If  I  am  correctly  informed,  at  the  Boleo  prop- 
erty in  Lower  California,  some  3O-ft.  furnaces  were 
erected,  were  found  unsatisfactory,  and  finally  divided 
into  two.  I  fear  that  a  furnace  of  this  kind  might  be 
much  like  the  Siamese  Twins,  with  one  having  a  con- 
gestive chill  and  the  other  a  burning  fever. 

Theoretically,  providing  the  hearth  area  were  the 
same,  a  circular  furnace  would  be  the  cheapest  to  con- 
struct, and  in  Arizona  they  still  consider  that  they  get 
better  results  from  an  elliptical  cross-section.  If  fur- 
naces were  made  narrow  and  long,  it  would  mean  in- 
creasing the  size  of  buildings,  particularly  if  the  furnaces 
were  put  end  to  end,  which  seems  to  be  the  best  method 
of  arranging  when  mechanical  charging  is  used.  If  this 

272 


7.  PARKE  CHANNING. 

point  is  taken  into  consideration,  I  think  that  the  total 
cost  of  the  plant  would  be  found  higher  than  in  the  case 
of  furnaces  approaching  a  square  in  their  cross-section. 
Our  experience  in  Tennessee  with  a  56-in.  by  i8o-in. 
furnace  has  been  very  satisfactory,  and  with  a  con- 
stantly increasing  tonnage,  so  that  we,  on  our  part,  are 
of  the  opinion  that  there  should  be  a  certain  ratio  be- 
tween length  and  width,  and  that  if  we  made  our  fur- 
naces, say,  240  in.  long,  it  would  be  well  to  increase  the 
width  to  66  in.  This,  however,  is  purely  .theoretical. 

At  the  Great  Falls  plant  of  the  Boston  &  Montana 
Company,  Mr.  Frank  Klepetko,  in  1896,  made  some 
extensive  experiments  with  three  furnaces,  each  180  in. 
long,  and  widths,  respectively,  42,  56  and  72  in.  The 
concensus  of  opinion,  after  several  months  of  experi- 
menting, was  that  the  56-in.  furnace  gave  the  best  re- 
sults, and  it  was  for  this  reason  that,  in  designing  the 
Tennessee  Copper  Company's  smelting  plant,  I  followed 
the  result  of  Mr.  Klepetko's  experiments.  The  relative 
tonnage  of  the  three  experimental  furnaces  at  Great 
Falls,  in  the  same  order  as  above  given,  was  330,  440 
and  400. 

Turning  now  to  the  question  of  coke  consumption,  we 
find  in  Tennessee  that  we  use  somewhat  less  coke  than 
our  neighbors,  the  Ducktown  Sulphur,  Copper  §c  Iron 
Company,  which  runs  small  Herreshoff  furnaces.  Cer- 
tainly at  Great  Falls  there  was  no  noticeable  difference 
in  the  coke  consumption  of  the  three  furnaces. 

It  certainly  would  take  more  men  on  the  feed  floor 
and  the  tapping  floor  to  run  five  .soo-ton  furnaces  than 
it  would  three  5oo-ton  furnaces,  even  assuming  that  the 
cost  of  charging  was  in  both  cases  the  same. 

As  regards  power  consumption  for  blast,  I  am  quite 
ready  to  admit  that  the  large  furnace  consumes  more 
horse-power,  but  I  am  of  the  opinion  that  this  increased 
cost  is  more  than  offset  by  other  advantages. 

To  say  that  mechanical  charging  is  not  defensible  is 

273 


PYRITR  SMELTING. 

tantamount  to  saying  that  we  should  not  replace  hand 
labor  by  machinery.  I  am  well  aware  that  metal- 
lurgists consider  that  a  hand-charged  furnace  will  run 
faster  than  one  in  which  the  material  is  irregularly 
dumped.  In  large  furnaces,  however,  it  is  not  as  appa- 
rent, and  the  top  of  the  charge  can  be  kept  level  almost 
as  well  as  in  a  small  hand-charged  furnace. 

In  the  month  of  January,  1903,  the  Tennessee  two- 
blast  furnaces  smelted  28,699  tons  of  charge  in  57-^  fur- 
nace days,  not  including  blast  furnace  products  re- 
smelted,  and  the  expense  was  as  follows : 

Coke,  0.1233  tons,  at  $4.93 $0.6082 

Quartz,  0.0958  tons,  at  $0.90 0.0862 

Supplies,  including  coal  for  power 0.1266 

Labor  and  superintendence 0.2111 

Total    $1.0321 

In  the  above  figures,  the  price  of  coke  is  abnormally 
high,  on  account  of  the  activity  of  the  Southern  iron 
market,  though  we  expect  that,  with  the  completion  of 
new  ovens,  the  price  will  return  to  a  normal  one  of 
about  $3.50. 

Labor  averages  about  $1.55,  so  that  we  may  assume 
about  0.14  of  a  shift  per  ton  of  ore.  This  includes,  in 
addition  to  the  furnace  labor,  the  proper  proportion  of 
surface  and  power-house  labor,  the  balance  going  to 
converter  expense. 

The  charging  expense  for  the  month  of  January, 
which  included  motormen,  car-loaders  and  dumpers,  re- 
pairs to  motors,  cars,  tracks  and  scales,  and  power  for 
operating  the  electrical  locomotives,  was  as  follows : 

Labor   $0.0340 

Supplies    0.0119 

Total    $0.0459 

I  doubt  very  much  if  hand  labor  could  in  any  way 
compete  with  these  figures,  or  whether  the  increased 
efficiency  of  the  furnace  would  more  than  counter- 
balance the  saving  in  handling  the  material. 

274 


/.  PARKE  CH ANN  ING. 

Our  slags  in  Tennessee  run  about  as  follows :  SiO2, 
31.54;  Cu,  0.49;  FeO,  52.25;  Mn,  0.79;  Zn,  2.02;  A12O3, 
3.50;  CaO,  5.93;  MgO,  1.86;  S,  1.25. 

I  cannot  forget  the  opening  sentence  of  the  late 
Prof.  Egleston,  in  his  first  lecture  to  me  as  a  student,  in 
which  he  said  that  "metallurgy  is  the  science  of  extract- 
ing money  from  ores."  I  fear  that  many  of  us  are  car- 
ried away  with  the  idea  that  high  tonnage  per  square 
foot  of  hearth  area,  or  low  slag,  is  what  we  are  striving 
for,  and  often  forget  the  commercial  side. 

J.  PARKE  CHANNING. 
New  York,  March  21,  1903. 


275 


CONTRIBUTION  BY  WILLIAM  A.  HEYWOOD. 

The  Editor : 

Sir — A  number  of  interesting  articles  on  tonnage  in 
copper  blast-furnace  smelting  have  appeared  recently 
in  The  Engineering  and  Mining  Journal,  and  doubtless  all 
metallurgists  are  interested  in  the  publication  of  the  re- 
sults obtained  at  different  smelters.  I  have  received  a 
number  of  letters  in  reply  to  my  communication  pub- 
lished July  26,  1902,  and  in  response  to  requests  for 
further  and  more  recent  information,  give  the  following 
record  of  the  work  done  at  the  Tennessee  Copper  Com- 
pany's smelter  during  the  month  of  February,  1903. 
Two  furnaces  were  in  blast  for  28  days,  and  smelted  as 
follows : 

Tons. 

Total  charge  smelted,  not  including  coke 30,095 

Total  ore  smelted 26,757 

Total  coke  used 3,269 

Charge  smelted  per  day  for  entire  month 1,074 

Charge  smelted  per  day  per  furnace 537 

The  average  slag  analysis  for  the  month  was:  In- 
soluble, 31.22  per  cent;  FeO,  51.39;  Cu,  0.44.  The  re- 
mainder is  mostly  alumina.  Our  ores  contain  little 
lime,  and  we  are  compelled  to  use  quartz  to  flux  the 
large  excess  of  iron.  On  account  of  the  high  specific 
gravity  of  these  irony  slags,  they'  carry  away  more 
copper  than  they  would  if  part  of  the  iron  were  replaced 
with  lime,  which  would  make  not  only  a  more  fusible 
but  a  lighter  slag.  The  average  number  of  men  and 
boys  employed  in  the  blast-furnace  department,  per  day 
of  24  hours,  is  54,  making  an  average  of  about  20  tons 
per  day  smelted  for  each  man  employed.  The  cost  of 


WILLIAM  A.  HEYWOOD. 

smelting  was  given  in  detail  in  The  Engineering  and  Min- 
ing Journal  of  February  14,  1903,  being  $1.05  per  ton  of 
ore  for  the  entire  year  1902.  Last  month,  notwith- 
standing coke  has  increased  in  cost,  the  smelting  cost 
was  under  that  figure. 

Following  is  a  summary  of  the  figures  given  in  the 
recent  articles  published  on  blast-furnace  smelting  ton- 
nages : 

||         !B|*     |&  |^ 

Name  of  Smelter.  Authority.  33  3  *tj*£      B        HOB 

Tenn.  Copper  Co.  (Feb. '03) 56  by  180  70  536  7.65 

" Two  Montana  Plants "  ...W.  B.  VanLlew  56  by  180  70  420  6 

Granby,  B.  C.  (Dec.  '01) . . .  .E.  Jacobs 44  by  160  49.5  354  7.1 

B.  C.  Copper  Co.  (Jan. '02). P.  Johnson....  42  by  150  48.7  428  9.8 

Old  Dominion  (5  days)....  W.B.  VanLlew  35  by  122  29.68  295  9.9 

Mr.  W.  R.  Van  Liew,  in  an  interesting  article  on 
'Ratio  of  Hearth  Area  to  Furnace  Capacity,'  states 
that  "tonnage  smelted  per  square  foot  of  hearth 
area  at  the  tuyeres  is  the  only  true  standard  by  which 
to  gauge,  or  compare,  the  workings  of  different  types 
of  furnace."  If  we  adopt  this  standard  the  above  table 
shows  the  results  to  be  in  favor  of  the  smaller  furnaces, 
not  because  they  smelt  more  tons  at  a  given  cost,  but 
because  they  have  a  smaller  divisor.  The  standard  I 
would  use  in  comparing  different  types  of  furnaces 
would  be  their  relative  economy.  As  conditions  vary 
at  every  smelter,  the  size  of  furnace  that  is  most  eco- 
nomical must  be  determined  by  actual  experiment.  Ton- 
nage is  only  one  of  the  elements  to  be  considered,  but 
so  far  the  experience  in  copper,  as  in  iron,  smelting  ap- 
pears to  indicate  that  the  large  furnaces  are  more  eco- 
nomical. 

I  cannot  agree  with  the  two  writers  who  have  re- 
cently mentioned  the  advantages  of  hand-feeding  over 
mechanical  feeding.  A  proper  system  of  mechanical 
feed  has  proved  so  much  more  economical  than  hand- 
feeding  that  it  is,  in  my  opinion,  merely  a  question 

277 


PYRITE  SMELTING. 

of  time  when  it  will  be  used  on  all  large  furnaces.  Re- 
garding the  claim  that  mechanical  feeding  produces 
stoppages  due  to  irregularities  in  the  running  of  the 
furnace,  1  would  state  that  the  last  campaign  of  our  No. 
i  furnace  lasted  6  months,  18  days,  during  which  time 
the  furnace  did  not  lose  a  single  shift,  and  smelted 
98,886  tons  of  material,  not  including  coke,  all  of  which 
was  fed  mechanically. 

WILLIAM  A.  HEYWOOD. 
Copperhill,  Tenn.,  March  24,  1903. 


278 


CONTRIBUTION  BY  GEORGE  W.  METCALFE. 

The  Editor : 

Sir — Following  out  the  suggestion  recently  made  in 
these  columns  as  to  the  publication  of  data  on  this  sub- 
ject, I  give  below  an  account  of  some  experiments  re- 
cently made  here  which  may  be  of  interest  to  the  pro- 
fession, though  not  yet  furnishing  sufficient  data  to  war- 
rant any  general  conclusion. 

The  blast-furnace  plant  here  was  designed  and  built 
in  accordance  with  the  results  of  the  Great  Falls  experi- 
ments of  Mr.  Klepetko,  mentioned  by  Mr.  Channing  in 
his  recent  letter ;  the  furnaces  were  56  by  180  in.  at  the 
tuyeres,  72  by  180  in.  at  the  top  of  the  jackets  and  18  ft. 
from  tuyeres  to  charging  floor.  The  method  of  charg- 
ing used  is  hand  dumping  of  large  coke  barrows  and 
mechanical  dumping  of  large  tram-cars  containing  ap- 
proximately 5,000  Ib.  each.  Materials  used  are  Butte 
ores,  coarse  concentrates  and  briquettes  of  flue  dust  and 
slime,  fluxed  by  converter  slag  and  limestone. 

On  first  starting  up  in  February,  1902,  considerable 
trouble  was  experienced  from  heavy  crusts  forming  on 
the  jackets,  both  ends  and  sides.  Much  of  the  end 
crusting  was  done  away  v/ith  by  cutting  off  the  end 
tuyeres — originally  there  were  12  tuyeres  in  front,  14  at 
the  back,  and  3  at  each  end — but  the  side  crusts  seemed 
to  be  due  to  improper  distribution  of  the  charge  caused 
by  the  partial  separation  of  its  coarse  and  fine  compo- 
nents by  sliding  from  the  car  over  a  sloping  charging 
plate  and  falling  three  or  four  feet  into  the  furnace. 
The  tendency  was  for  the  larger  and  heavier  fragments 
to  fall  in  the  center,  the  finer  materials  remaining  at  the 

279 


PYRITE    SMELTING. 

sides.  The  higher  this  drop  the  more  pronounced  the 
sorting  action ;  so,  as  the  natural  expedient  of  keeping 
the  furnaces  full  was  found  to  make  even  worse  crusts, 
the  experiment  was  tried,  in  building  two  new  furnaces, 
of  making  them  respectively  3  ft.  and  6  ft.  lower  than  the 
original  five  furnaces.  At  the  same  time,  as  it  was 
the  intention  to  run  with  less  depth  of  charge  and  lower 
blast  pressure,  the  jackets  were  drawn  in  at  the  bottom 
so  as  to  make  these  furnaces  48  in.  instead  of  56  in. 
wide. 

\. 

Blast  used  on  the  original  five  furnaces  was  28  to 
30  oz.,  on  the  No.  6  (15  ft.  deep)  26  oz.,  and  on  the 
No.  7  (12  ft.  deep)  24  oz.  Other  blast  pressures  were 
used  at  times,  but  these  were  finally  settled  on  as 
yielding  the  best  results. 

During  a  six  weeks'  run  No.  7  furnace  (12  ft.  deep) 
averaged  352  tons  of  charge  per  day  on  10.2  per  cent 
of  coke,  while  four  furnaces  of  the  original  type  in  that 
time  averaged  397  tons  of  charge  per  day  on  9.8  per 
cent  coke.  During  this  period  a  constant  attempt  was 
made  to  run  No.  7  on  the  same  charge  and  coke  per- 
centage as  the  other  furnaces,  but  it  invariably  became 
crusted  badly,  and  had  to  be  put  on  a  more  fusible  and 
ferruginous  charge  with  a  higher  coke  per  cent  until 
the  crusts  were  burned  out.  However,  during  all  this 
period,  as  was  expected,  it  made  about  4  per  cent  better 
matte  than  the  others,  which  averaged  40.4  per  cent 
copper.  The  average  slag  of  all  the  furnaces  assayed : 
Cu,  0.19  per  cent;  SiO2,  43.3;  FeO,  26.0;  CaO,  21.8, 
and  A12O3,  8  per  cent. 

During  another  six  weeks'  run  No.  6  furnace  (15  ft. 
deep)  averaged  383  tons  per  day  on  9.7  per  cent  coke, 
while  the  four  furnaces  of  the  original  type  averaged 
407  tons  per  day  on  9.6  per  cent  coke,  all  the  furnaces 
being  practically  all  the  time  on  the  same  charge.  No. 
6  made  matte  averaging  42.6  per  cent  copper,  the  aver- 

280 


GEORGE  W.  METCALFE. 

age  of  the  others  being  39.7  per  cent  copper.  The  slags 
of  all  the  furnaces  averaged:  Cu,  0.18  per  cent ;  SiO2, 
44.0;  FeO,  26.0}  CaO,  21.8;  A12O3,  6.8. 

During  four  of  the  six  weeks  of  this  latter  experi- 
ment No.  3  furnace  also  had  the  jackets  drawn  in  to 
make  the  size  48  by  180  in.  at  the  tuyeres,  though  re- 
maining as  before  18  ft.  in  depth.  During  that  time  it 
averaged  397  tons  per  day  on  9.3  per  cent  coke,  while 
the  three  unaltered  i8-ft.  furnaces  averaged  409  tons  on 
9.6  per  cent  coke.  The  No.  3  matte  averaged  0.5  per 
cent  less  than  the  56  by  180  in.  furnaces.  Fed  high  and 
blown  the  same  as  the  others  it  would  nearly  keep  up  in 
tonnage,  but  it  made  the  lower  grade  of  matte ;  with 
less  blast,  even  down  to  20  oz.,  and  fed  low  it  still  made 
0.5  per  cent  poorer  matte,  and,  of  course,  fell  still 
further  behind  in  tonnage. 

The  above  figures  as  to  tonnage  are  compiled  from 
our  charge  foreman's  reports.  The  actual  amounts 
smelted,  owing  to  our  method  of  loading  the  charges, 
always  ran  about  10  per  cent  more  after  being  checked 
up  by  the  railroad  weights ;  quite  the  contrary  result 
from  that  obtained  by  most  plants  on  checking  against 
railroad  weights. 

None  of  these  changes  seemed  to  have  any  appre- 
ciable effect  in  lessening  the  crusts  in  the  upper  part  of 
the  furnaces,  though  the  i8-ft.  furnace  contracted  to 
48  by  180  in.  at  the  tuyeres  kept  hotter  and  in  better 
shape  at  the  bottom.  We  have,  however,  as  the  feeders 
became  more  accustomed  to  the  system  of  charging, 
usually  been  able,  on  all  the  furnaces,  to  prevent  the 
formation  of  such  crusts  as  would  seriously  retard  their 
running. 

In  the  experiments  on  No.  6  and  No.  7  furnaces  the 
differences  in  depth  interfere  somewhat  with  drawing  a 
conclusion  as  to  the  effect  of  the  narrower  width  per  se ; 

281 


PYR1TE  SMELTING. 

while  the  results  on  No.  3,  though  showing  a  decided 
increase  in  tonnage  per  square  foot  of  hearth  area,  cer- 
tainly do  not  indicate  that  the  narrower  width  is  per  se 
a  commercial  advantage  in  smelting  our  materials. 
However,  the  results  on  No.  6,  showing  a  slightly  de- 
creased tonnage  but  an  increased  grade  of  matte,  and  a 
slightly  decreased  power  expense,  owing  to  the  lower 
blast  pressure,  may  readily  be  held  to  indicate  a  com- 
mercial advantage  for  the  48  by  180  in.  furnace  of  15  ft. 
depth  in  a  plant  where  cost  of  converting  is  an  impor- 
tant item. 

Our  experience  here  leads  me  to  differ  from  Mr.  Van 
Liew  as  to  the  advantage  of  mechanical  charging.  Until 
1902  we  were  here  running  a  number  of  furnaces  45  by 
100  in.  at  the  tuyeres  and  n  ft.  from  tuyeres  to  charg- 
ing floor.  Pretty  much  the  same  materials  were  used 
as  in  the  56  by  180  in.  furnaces  now  in  use,  but  in 
slightly  different  proportions;  the  small  furnaces  using 
about  38  per  cent  raw  ore,  32  per  cent  of  slag  and  matte, 
and  30  per  cent  of  limestone,  and  making  a  slag  con- 
taining about  39  per  cent  biO2,  26.6  FeO,  and  22  CaO ; 
while  the  large  furnaces  use  about  45  per  cent  of  raw 
ore,  27  per  cent  of  slag  and  matte  and  28  per  cent  of 
limestone,  and  make  a  slag  containing  about  42.5  per 
cent  SiO2,  26.9  FeO,  and  21.2  CaO.  The  small  furnaces 
were  fed  from  small  hand  barrows,  but  so  skillfully  that 
they  were  kept  practically  free  from  crusts,  while  the 
large  furnaces  are  fed  from  cars,  as  described  above, 
and  are  generally  somewhat  crusted.  The  large  fur- 
naces use  a  larger  coke  per  cent,  though  a  comparison 
of  the  materials  used  would  not  indicate  that  this  is  en- 
tirely due  to  the  mechanical  feeding.  However,  the 
cost-sheets  show  that  the  excess  in  coke  costs  on  the 
large  furnaces  is  considerably  more  than  balanced  by 
the  excess  in  labor  costs  on  the  small  furnaces,  while 
the  larger  furnaces  get  a  still  further  advantage  in  the 
final  cost  per  ton  from  the  large  divisor  that  their  heavy 

282 


GEORGE  W.  METCALFE. 

tonnage  gives  them  into  the  general  expenses  of  the 
plant. 

I  think  further  data  from  plants  smelting  the  same 
materials,  in  different  models  of  furnaces,  would  be  very 
generally  appreciated. 

GEORGE  W.  METCALFE. 
Anaconda,  Mont.,  April  10,  1903. 


288 


CONTRIBUTION  BY  JAMES  W.  NEILL. 

The  Editor: 

Sir — The  interesting  article  by  Mr.  Van  Liew  in  your 
issue  of  the  21st,1  touches  upon  a  point  in  smelting  prac- 
tice of  vital  interest  to  practical  men.  The  question, 
"How  wide  should  a  blast  furnace  be  to  treat  a  certain 
ore?"  is  not  so  readily  answered,  nor  will  mere  refer- 
ence to  the  workings  of  other  furnaces  always  be  a  safe 
guide.  The  quality  of  the  ore  to  be  smelted  and  the  re- 
sults to  be  obtained  must  be  considered,  and  the  fur- 
nace should  conform  to  these.  The  different  furnaces 
mentioned  by  Mr.  Van  Liew  are  handling  very  different 
materials,  thus:  In  Montana  the  material  is  crude  ore, 
coarse  in  size,  very  silicious,  carrying  12  to  15  per  cent 
sulphur.  The  fluxes  are  either  coarse  concentrate  or 
coarse  iron  ore,  and  coarse  limestone.  Briquetted 
material  is  included.  This  charge  produces  a  very  sili- 
cious slag  and  matte  of  converter  grade.  In  British 
Columbia,  Mr.  Johnson  has  been  smelting  a  crude  ore 
consisting  chiefly  of  metamorphosed  limestone  (con- 
taining garnet,  epidote,  etc.)  with  much  magnetite  and 
very  small  amounts  of  sulphides,  so  that  there  is  no 
sulphur  to  be  eliminated;  the  ore  is  a  "natural  flux." 
Moreover,  it  is  broken  in  surface  quarries  and  arrives  at 
the  smelter  in  large,  coarse  pieces,  ideal  for  blast-fur- 
nace work. 

In  Tennessee,  Mr.  Channing  is  smelting  a  heap- 
roasted  pyrrhotite,  which  is  low  in  silica,  requiring  the 
addition  of  quartz  for  good  slag  results.  This  material 
again  is  in  large  pieces,  porous  from  the  roasting  oper- 
ation, and  in  most  excellent  condition  for  the  blast  fur- 
nace. Here,  again,  the  amount  of  sulphur  to  be  driven 

i  See  page  2  66. 

284 


JAMES  W.  NEILL. 

off  in  the  furnace  is  considerable.  The  slag  is  naturally 
an  irony  one,  but  the  resulting  matte  is  of  converter 
grade. 

At  the  Globe  plant,  in  Arizona,  the  regular  work  of 
the  furnace  has  evidently  been  the  production  of  black 
copper  from  oxidized  ores,  and  the  test  made  by  Mr. 
Van  Liew  was  for  the  purpose  of  producing  matte  in- 
stead. It  is  evident  from  the  context  that  the  amount 
of  sulphides  used  in  this  5-day  run  was  no  more  than 
necessary  to  cover  the  copper  and  produce  matte,  there- 
fore no  sulphur  to  speak  of  would  have  been  driven  off. 
I  do  not  know  the  conditions  as  to  the  size  of  ore  par- 
ticles when  fed  to  furnace. 

If  instead  of  the  conditions  described  we  consider 
an  ore  which  contains  35  per  cent  sulphur  (as  pyrite), 
which  breaks  in  the  mine  so  fine  that  it  resembles  con- 
centrate (60  per  cent  will  pass  a  f-in.  screen),  and  carries 
silica  sufficient  to  flux  the  iron ;  under  such  conditions, 
what  width  of  furnace  should  I  use?  The  data  given 
by  Mr.  Van  Liew  do  not  help  me,  as  the  conditions  are 
not  similar  to  any  of  those  cited.  We  cannot  heap- 
roast  ;  and  mechanical  roasting  will  necessitate  briquet- 
ting,  which  we  desire  to  avoid. 

It  is  obvious  that  to  charge  such  fine  material  into  a 
blast  furnace  56  in.  in  width,  will  result  in  a  very  heavy 
body  of  material,  through  which  the  blast  will  penetrate 
with  difficulty  and  necessitate  a  high  pressure.  This  will 
result  in  the  formation  of  'blow-holes'  and  all  the  at- 
tendant troubles  known  to  the  practiced  blast-furnace 
man,  with  the  production  of  immense  quantities  of  flue- 
dust  and  flue  losses.  Furthermore,  high  pressure  is 
the  surest  agent  toward  reducing  action  in  the  furnace, 
but  in  this  very  case  we  desire  oxidizing  action,  or  our 
matte  will  be  too  low  in  grade !  Therefore,  such  con- 
ditions, more  than  the  question  of  buildings  or  of  pre- 
vious records,  must  govern  our  choice  of  furnace  width. 

I  do  not  think  that  the  data  given  by  Mr.  Van  Liew 

285 


PYRITE  SMELTING. 

warrant  the  deduction  that  a  narrow  furnace  will  always 
smelt  more  tons  per  square  foot  of  hearth  area;  the 
physical  conditions  of  the  ore  charge  and  its  chemical 
contents  must  be  largely  factors  in  the  final  result. 
Thus,  for  the  Old  Dominion  ores  making  black  copper 
I  should  choose  a  round  or  elliptical  furnace;  for  the 
porous  Tennessee  ores,  any  length  and  width  which  my 
blast  would  penetrate ;  in  Butte  not  over  45  in.  in  width, 
and  for  the  fine  sulphides  mentioned  above  not  over  42 
in.,  with  a  preference  for  less. 

JAMES  W.  NEILL. 
Salt  Lake  City,  Utah,  March  26,  1903. 


REVERBERATORY  COPPER  SMELTING. 

By  E.  P.   MATHEWSON. 

Probably  the  largest  installation  of  reverberatory 
furnaces  built  in  recent  years  for  the  smelting  of  copper 
is  that  of  the  Washoe  Copper  Co.,  at  Anaconda,  Mont. 
The  plant  consists  of  14  furnaces,  originally  20  by  50  ft. 
hearth  measurement,  set  back  to  back  in  two  rows,  and 
housed  in  two  steel  buildings  substantially  built  and 
well  ventilated.  Between  these  buildings  is  a  chimney 
225  ft.  high,  20  ft.  internal  diameter,  constructed  of  steel 
and  lined  with  brick,  the  connections  to  the  furnaces 
being  made  by  four  main  flues.  One  feature  of  the 
original  construction  was  an  arrangement  for  pre-heat- 
ing  the  air  by  the  heat  of  the  escaping  gases  and  the 
heat  radiated  from  the  bottom  of  the  hearth.  The  air 
was  admitted  first  to  a  brick  chamber  built  around  the 
brick-lined  steel  pipe,  which  carried  the  waste  gases  to 
the  main  flue ;  thence  the  partially  heated  air  passed  be- 
neath the  bottom  of  the  furnace  in  a  narrow  channel, 
passing  from  the  front  to  the  back  four  times  before 
rising  in  a  cast-iron  box  to  the  top  of  the  furnace; 
thence  to  a  sheet-steel  box  above  the  bridge  wall,  being 
finally  admitted  to  mix  with  the  gases  from  the  fire-box, 
through  checker  work  in  the  roof  above  the  bridge  wall, 
the  draft  of  the  furnace  being  sufficient  to  draw  in  the 
hot  air.  In  remodeling  the  furnaces,  this  arrangement 
was  omitted,  as  it  was  considered  more  important  to 
retain  the  heat  in  the  bottom  of  the  furnaces  than  to 
use  it  for  pre-heating  the  air  furnished  to  the  top  of  the 
charge,  more  rapid  smelting  being  accomplished  by 
keeping  the  matte  in  the  furnace  as  hot  as  possible. 

In  building  the  plant,  every  convenience  to  facilitate 

287 


PYRITE    SMELTING. 

the  handling  of  materials  was  arranged  for.  The  ashes 
from  ash-pits  are  sluiced  away  by  waste  water  from  the 
concentrating  department,  and  the  slags  are  granu- 
lated and  washed  away  to  the  dump  by  the  same  means. 
The  matte  is  tapped  from  time  to  time  into  large  ladles 
holding  ii  tons  and  drawn  by  compressed-air  locomo- 
tives to  the  converting  department,  where  the  still 
molten  matte  is  dumped  from  ladle  to  converter  to  be 
blown  to  copper.  The  air  necessary  for  the  combus- 
tion of  the  fuel  was  forced  under  the  grates  by  fans,  the 
ash-pit  being  closed  by  cast-iron  doors.  Each  furnace 
had  an  average  daily  smelting  capacity  of  100  tons  of 
calcines.  The  fuel  used  was  obtained  from  Diamond- 
ville,  Wyo.,  and  consisted  of  'run-of-mine'  coal  of  the 
following  composition:  water,  1.6;  volatile  combustible, 
38.7;  fixed  carbon,  49.2;  and  ash,  10.5  per  cent.  This 
coal  gives  very  satisfactory  results  under  natural  draft, 
but  with  forced  draft  it  does  not  act  so  well. 

In  the  former  practice  the  time  lost  in  grating  the  fur- 
nace averaged  three  hours  per  day  per  furnace,  and 
during  the  grating  (which  occupied  one-half  hour  at  a 
time)  the  front  of  the  furnace  became  cooled  and  the, 
slag  frequently  set  near  the  skimming-door.  At  the 
suggestion  of  Capt.  W.  M.  Kelly,  Furnace  No.  Q  was  re- 
modeled on  the  lines  of  the  best  furnace  at  the  old  Ana- 
conda works,  and  an  extra  large  fire-box  was  con- 
structed in  order  to  give  every  chance  possible  for  the 
furnace  to  work  without  forced  draught.  The  grates 
were  ordinary  bar  iron,  with  open  ash-pit.  The  flues 
were  changed  to  permit  of  a  more  direct  connection 
without  sharp  bends,  and  the  down-takes  for  escaping 
gases  were  enlarged.  The  results  obtained  in  the  modi- 
fied furnace  were  excellent  at  the  start,  and  the  good 
record  has  been  satisfactorily  maintained. 

In  consequence  of  the  improvements  in  furnace  No. 
9,  the  other  furnaces  were  altered  accordingly,  and  the 
working  under  the  new  conditions  made  a  very  excel- 

288 


E.  P.  MATHEWSON. 

lent  showing,  as  set  forth  by  the  following  data :  Aver- 
age tonnage  of  calcines  treated  per  furnace  per  day  was : 
January,  1903,  106.6;  February,  115.7  tons;  March, 
123.84  tons;  and  April,  133.53  tons.  The  fuel  con- 
sumption averaged  one  ton  of  coal  to  three  tons  of  cal- 
cines treated,  and  it  may  be  stated  that  this  good  aver- 
age will  be  still  further  improved.  The  total  supply  of 
coal  delivered  to  the  plant  is  charged  up  as  weighed, 
and  during  the  months  under  review  (January  to  May, 
1903)  much  of  this  coal  was  consumed  in  starting  up 
new  furnaces  and  in  tapping  out  old  ones.  The  best 
record  for  fuel  consumption  yet  obtained  on  a  single 
furnace  is  I  ton  of  coal  to  4.07  tons  of  calcines,  the  out- 
put of  the  furnace  being  171  tons.  Under  the  present 
conditions  the  furnaces  carry  an  even  heat,  and  no  time 
is  lost  in  grating.  The  materials  sent  to  each  furnace 
are  carefully  weighed  in  charge  cars  (20  tons  to  the 
charge),  which  are  again  weighed  when  empty  each 
trip.  The  weighing  and  tramming  are  done  by  a  set  of 
men  entirely  separate  from  the  furnace  crew  and  under 
a  separate  foreman.  The  coal  weights  are  checked 
monthly  by  the  railroad  car  weights  and  check  within 
1.5  per  cent  of  the  latter — the  variation  being  over- 
weight. All  material  for  the  furnaces  is  handled  by 
compressed-air  locomotives,  and  is  loaded  in  hopper- 
bottom  cars  which  discharge  into  the  hoppers  above  the 
furnaces. 

Under  the  improved  conditions  of  working,  the  ag- 
gregate cost  of  coal,  labor  and  repairs  has  been  re- 
duced by  more  than  $1,000  per  day.  The  following 
details  of  furnace  operations  are  of  interest :  Draft  in 
down-take  =1.5  in.  of  water.  Analysis  of  material 
charged:  Cu,  10.5  per  cent;  SiO2,  33.2;  FeO,  39.5, 
and  S,  7.8  per  cent.  Analysis  of  slag  produced:  Cu, 
0.39  per  cent;  SiO2,  41.4;  FeO,  45.8,  and  CaO,  3.1  per 
cent.  Copper  content  of  matte  produced  47.44  per 
cent. 

239 


PYRITE    SMELTING. 

During  March,  1903,  three  of  the  old-style  furnaces 
were  still  in  operation,  which  reduced  the  average  ton- 
nage. The  modified  furnace  treated  on  the  average 
135  tons  of  calcines  per  day,  and  each  of  the  old  fur- 
naces when  remodeled  will  have  a  capacity  of  140  tons 
per  day,  with  fuel  consumption  of  I  ton  of  coal  to  3.5 
tons  of  calcines  smelted.  Another  important  change 
now  being  installed  is  the  placing  of  a  3OO-h.  p.  Stir- 
ling boiler  between  each  reverberatorv  furnace  and  the 
main  flue,  the  idea  being  to  utilize  the  waste  heat  of  the 
gases  escaping  from  the  furnaces.  These  boilers  have 
been  tried  once  before  at  the  plant,  but  they  were  then 
installed  in  the  same  manner  as  for  direct  coal-firing, 
and  although  the  boilers  themselves  made  excellent 
records,  the  output  of  the  furnaces  to  which  they  were 
attached  fell  20  per  cent  below  those  that  had  no  boilers. 
In  the  new  setting,  the  idea  has  been  to  give  free  pass- 
age through  the  boiler,  and  ample  down-take  beyond, 
in  order  to  facilitate  the  escape  of  gases  as  much  as 
possible.  Furnace  No.  n,  which  was  arranged  in  this 
manner,  has  given  excellent  results,  the  draft  on  each 
side  of  the  boiler  corresponding  to  1.6  in.  of  water. 
The  temperature  of  the  gases  at  the  inlet  of  the  boiler 
was  2,380°  F.,  while  at  the  outlet  it  was  1,100°  F.  Allow- 
ing 34.5  Ib.  of  water  per  horse-power-hour  from  and  at 
212°  F.,  and  feeding  the  water  at  47.2°  F.,  the  boiler 
tested  340  h.  p.,  which  corresponded  to  a  saving  in  coal 
alone  of  $70  per  boiler  per  day.  The  steam  pressure 
was  155.7  rt>.  on  an  average. 

On  account  of  more  careful  mixing  and  fluxing  of  the 
charge  in  the  McDougal  calciners,  the  tonnage  smelted 
in  the  reverberatory  furnace  averaged  172.3  daily  in 
January,  1904,  with  a  coal  ratio  of  3.53  to  I.  Early  in 
1904  No.  6  reverberatory  was  rebuilt  with  hearth  IQ  ft. 
by  59  ft.  1.5  in.  This  furnace  now  averages  207  tons 
daily,  with  a  coal  ratio  of  4.33  to  I,  developing  416  boiler 
h.  p.  steam. 

290 


E.  P.  MATHEWSON. 

As  No.  6  was  a  success,  No.  i  and  2  were  dismantled, 
and  a  new  No.  i  built  with  fire-box  7  by  16  ft.,  hearth 
19  ft.  by  83  ft.  2  in.,  and  two  Stirling  375-h.  p.  boilers  set 
tandem.  This  furnace  averages  241  tons  daily,  with  a 
coal  ratio  of  4.53  to  I,  and  develops  710  boiler  h.  p., 
its  record  performance  being  305  tons,  with  coal  ratio 
5.25  to  i.  The  next  move  was  to  replace  the  No.  7  and 
8  furnaces  with  one  called  No.  4,  with  fire-box  7  by  16 
ft,  and  hearth  19  ft.  by  102  ft.  9  in.,  with  two  boilers  tan- 
dem, as  in  No.  i.  This  furnace  has  not  been  in  opera- 
tion long  enough  to  determine  its  capacity,  but  it  has 
smelted  333  tons  with  a  record  coal  ratio  of  5.28  to  I, 
beside  developing  720  boiler  h.  p.  steam.  The  tempera- 
ture of  escaping  gases  was  590°  F.  An  experimental  jig- 
ging plant,  to  treat  the  ashes  from  No.  I  furnace,  is  in 
successful  operation,  saving  5.8  tons  of  fine  coke  daily 
(n  per  cent  ash),  which  is  being  briquetted  with  slimes 
from  the  concentrator,  and  fed  into  blast  furnaces  with 
a  corresponding  saving  in  fuel  in  that  department.  A 
jigging  plant  situated  so  as  to  take  the  ashes  from  all 
the  reverberatory  furnaces  is  now  being  installed. 


291 


MATTING    OF    ORES    AT    LEADVILLE    AND 
ROBINSON,  COLORADO.1 

BY  C.  H.  DOOLITTLE.1 

In  presenting  these  notes  to  the  profession  it  is  with 
the  view  of  counteracting  some  ideas  concerning  cap- 
acity of  furnace,  upon  which  great  stress  has  been  laid 
during  the  past  year  in  various  articles  appearing  in 
The  Engineering  and  Mining  Journal. 

The  writer  has  visited  some  of  the  works  possessing 
furnaces  with  such  large  capacities,  and  he  has  been  em- 
ployed at  both  matting  and  lead-smelting  plants  in  this 
country  and  Mexico,  so  that  he  is  frank  enough  to  con- 
fess that  no  individual  problem  has  been  a  harder  one 
to  solve  than  the  one  at  Leadville,  and  its  success  was 
due  in  a  great  measure  to  its  vice-president  and  general 
manager,  the  late  Mr.  Franklin  Ballou.  The  two  plants 
are  now  closed,  the  Bi-Metallic  having  been  sold  to  the 
American  Smelting  and  Refining  Company,  while  the 
Robinson  smelter  is  closed  down,  pending  the  further 
development  of  the  mines.  Leadville  during  the  year 
1900,  the  period  to  which  these  notes  refer,  was  dull, 
with  the  market  conditions  such  that  suitable  ores  were 
difficult  to  obtain — copper  sulphides  very  scarce  and 
zincy  iron  sulphides  predominating. 

The  tonnage  of  a  furnace  is  due  both  to  the  physical 
and  the  chemical  condition  of  the  ores  which  are  treated. 
The  Leadville  ores  are  naturally  fine,  and  it  would  ap- 
pear as  if  too  much  powder  was  used  in  mining,  but  the 

*The  Engineering  and  Mining  Journal,  April  11. 1903,  page  558. 

£  s«Pe"ntendent  of   the  Bi-Metallic   Smelter,   at  Leadville    Colo, 
the   Robinson   Construction  Mining   &   Smelting   Co.,    at   Robinson' 

292 


C.  H.  DOOLITTLE. 

mine  owner  prefers  to  ship  his  ore  in  that  condition, 
claiming  that  it  helps  accurate  sampling.  One-tenth 
sometimes,  one-fifth  more  frequently,  had  to  be  crushed, 
rolled  and  sampled,  and  for  a  month  at  a  time  our  flue- 
dust  and  slimes  amounted  to  one-tenth  of  the  total  ore. 
It  is  likely  that  Mr.  Herbert  Lang  must  have  had  some 
experience  of  this  kind,  as  he  assumed  that  the  Ten- 
nessee Copper  Company  was  doing  similar  work,  but 
very  much  to  my  surprise,  on  a  visit  to  that  company's 
works,  the  writer  could  find  but  little  flue-dust,  and,  in 
fact,  they  were  making  less  than  0.5  per  cent,  as  nearly 
as  could  be  figured  without  actual  weighing. 

I  would  like  at  this  point  to  contradict  a  statement 
frequently  heard,  that  "anybody  can  run  a  copper-mat- 
ting furnace,  but  it  takes  a  good  man  to  run  a  lead  fur- 
nace." I  have  had  more  sleepless  nights  over  the 
former  than  the  latter,  and  with  a  copper-matting  fur- 
nace with  an  ore  column  of  6  to  7  ft.,  and  the  ores  as 
rich  in  silver  and  gold  as  the  average  lead  smelter,  and 
rustling  hard  to  get  1.5  per  cent  of  copper  in  the  charge, 
the  superintendent  must  be  up  early  and  late,  and  not 
sleep  far  from  the  furnace. 

The  Bi-Metallic  plant  was  unique  in  several  features, 
and  the  system  adopted  was  worked  out  after  much 
hard  labor  and  expense.  The  furnaces  were  three  in 
number,  having  the  dimensions,  at  the  tuyeres,  of  36  by 
163  in.,  36  by  175  in.,  and  36  by  215  in.  The  first  two 
were  used  for  concentrating  the  ore  into  a  low-grade 
matte,  the  third  and  largest  one  for  reconcentrating  the 
matte  with  the  addition  of  oxidized  silicious  ores.  The 
air  was  furnished  cold  by  three  No.  7  Root  blowers,  and 
so  connected  to  the  furnaces  that  each  furnace  could 
have  its  individual  blower,  or  they  could  be  turned  into 
the  general  main,  and  the  blast  drawn  and  subdivided 
for  the  various  furnaces.  The  individual  arrangement 
was  found  preferable.  Two  fans,  one  9  ft.  and  one  6  ft. 

293 


PYRITE    SMELTING. 

diameter,  were  connected  with  the  dust  chamber;  the 
gases,  after  having  traveled  300  ft.,  were  forced  through 
towers,  where  they  were  sprayed,  and  a  large  part  of  the 
fume,  rich  in  lead  and  silver,  was  precipitated  and  saved. 
The  gases  then  escaping  were  damp  and  reduced  to  a 
temperature  of  100°  F.,  which  necessitated  a  wooden 
stack.  The  power  was  furnished  by  a  Corliss  engine 
developing,  by  card  measurement,  450  horse-power  as 
its  maximum  load. 

Having,  by  experience,  found  the  capacity  of  the 
various  furnaces  for  ore  and  matte,  we  endeavored  to 
so  run  the  furnaces  that  the  matte  produced  by  the  ore 
furnaces  was  just  sufficient  for  the  reconcentration 
furnace,  and  the  slag  from  the  reconcentration  furnace, 
which  had  to  be  re-smelted,  was  not  too  burdensome 
for  the  ore  furnaces,  but  still  sufficient  for  keeping  an 
open  charge  in  the  ore  furnaces.  We  thus  endeavored 
to  keep  our  capital  out  of  large  surpluses  of  low  matte 
and  high  slag. 

The  characteristic  ores  treated  are  given  in  the  fol- 
lowing table : 

Name  of  Mine.  SiOa          Fe          CaO          Zn  Cu 

(Wet.) 

Iron  Silver 3.  41.  0.  6.              .1 

Ibex  M.  Co 20.  28.  0.  6.  2.7 

New  Monarch   28.  18.  0.  11.  3.5 

Marian    8.  38.  0.  1.             .5 

Vinnie 23.  23.  0.  9.  3. 

Commodore 85.  3.  2.  0.  0. 

Centennial-Eureka    .  .  77.  5.  2.  2.  6. 

During  the  month  of  March,  1900,  the  three  fur- 
naces ran  31  days  each,  and  there^  was  treated  9,838  tons 
of  ore,  carrying  2,256  oz.  Au,  159,811  oz.  Ag,  314,690 
Ib.  Cu.  This  shows  an  average  for  the  three  furnaces 
of  105.8  tons  of  ore  per  furnace  per  day.  The  matte 
shipped  averaged  2,249  oz-  Au,  146  oz.  Ag,  14,328 
per  cent  copper.  The  recovery,  98.5  per  cent  Au,  95 
per  cent  Ag,  90  per  cent  copper. 

294 


C.  H.  DOOLITTLE. 
A  charge  for  the  ore  furnace  consisted  of : 

Lb. 

Ore    (all   sulphides) 2,600 

Lime  rock 250 

Bricked  flue-dust    300 

Slag 1,500 

Coke    325 


Total    4,975 

This  shows  a  consumption  of  fuel  of  12.5  per  cent  on 
the  ore,  but  such  was  not  really  the  case,  as  the  works 
were  supplied  with  a  method  of  submerging  the  coke  in 
water,  and  it  carried  20  per  cent  moisture;  hence  the 
actual  percentage  of  coke  was  10  per  cent. 

The  flue-dust  was  bricked  and  fed  in  sufficient  quan- 
tities to  keep  that  objectionable  material  (and  necessarily 
a  large  one  at  this  point)  from  accumulating.  The  slag 
specified  above  came  from  the  re-concentration  furnace, 
and  was  fed  to  keep  this  stock  low  and  the  charge  open. 
Under  ordinary  conditions  the  ore  furnaces  averaged 
120  tons  of  ore  each.  Great  care  had  to  be  used  in 
feeding  the  furnace,  on  account  of  the  fine  ore  and  the 
heating  qualities  due  to  the  sulphur.  A  charge  for  the 
concentrating  furnace  consisted  of : 

Lb. 

Matte    1,000 

SiHcious  ore 600 

Lime  rock    100 

Wet  coke   125 

Total    1,825 

This  shows  a  consumption  of  fuel  (dry)  of  16  2-3  per 
cent.  Taking  the  whole  number  of  tons  of  ore 
treated  for  the  month  of  March,  9,838,  and  the  actual 
amount  of  fuel  consumed,  1,417  tons,  gives  a  fuel  con- 
sumption per  ton  of  ore  of  14.4  per  cent,  which  is  a 
proper  average  for  a  year,  as  well  as  for  this  month. 

The  capacity  of  this  furnace,  for  ore,  was  75  tons  per 
day.  The  average  slag  was :  SiO2,  36  per  cent ;  Fe,  36 
per  cent;  CaO,  7  per  cent;  Zn,  5  per  cent.  A  little 
higher  saving  might  have  been  made  by  the  addition  of 

295 


PYRITE    SMELTING. 

more  lime  and  using  less  iron ;  but  from  a  commercial 
standpoint,  lime  cost  us  money,  and  a  $9  rate,  on  a 
neutral  basis,  on  iron  ore,  left  a  good  margin  for  treat- 
ing that  class  of  ore.  The  average  cost  for  the  month 
showed  $3.645  per  ton  of  ore  treated,  including  all  ex- 
penses, except  new  construction.  The  matte  was 
shipped  to  the  Philadelphia  Smelting  and  Refining  Com- 
pany, at  Pueblo,  and  treated  for  $3.25  (freight  and  treat- 
ment), allowing  us  $19.25  per  oz.  for  Au,  95  per  cent  of 
the  Ag,  4c.  off  casting  brand  quotation  for  copper. 

The  Robinson  Construction,  Mining  and  Smelting 
Company  had  but  one  stack,  though  a  second  one  was 
on  the  ground  ready  for  erection.  This  is  a  36  by  142  in. 
Loder  hot-blast  furnace.  The  hot  blast  consists  simply 
of  a  series  of  pipes  carrying  the  air  in  a  chamber  through 
which  the  escaping  gases  from  the  furnace  pass  on  their 
way  to  the  dust  chamber.  The  blast  is  warmed,  and  the 
highest  temperature  obtained  from  numerous  tests  was 
200°  F.,  but  even  this  is  not  to  be  despised  if  it  can  be 
obtained  without  unnecessary  use  of  over-feeding  fuel. 
During  the  times  of  re-concentration  the  furnace  was 
always  run  with  a  cool  top  to  avoid  losses  in  precious 
metals ;  then  the  blast  temperature  would  drop  to  about 
90°  F.  The  conditions  at  this  plant  were  more  favor- 
able to  smooth  running  than  at  Leadville.  We  mined 
our  own  ores  and  lime-rock,  hence  we  were  able  to  keep 
the  physical  condition  of  the  ores  such  that  slag  was 
not  a  necessity  to  keep  the  charge  open. 

The  chemical  conditions  were  different,  in  that  copper 
appeared  in  the  ores  we  mined  only  as  traces,  and  but  a 
small  amount  of  copper  ore  was  obtainable  on  the  mar- 
ket, and  this  ran  but  4  per  cent  Cu,  so  our  collector  was 
practically  an  iron  matte ;  but  we  made  a  good  saving, 
which  was  due  partly  to  the  copper  and  more  to  a  heavy 
fall  of  matte.  The  specific  gravity  of  the  slag  was  light- 
ened by  a  higher  percentage  of  lime  than  at  Leadville. 
The  market  condition  for  the  sale  of  matte  had  changed. 

296 


C.  H.  DOOLITTLE. 

There  was  no  competition,  and  but  one  purchaser  for 
our  matte.  The  price  paid  was  $9.45  freight  and  treat- 
ment, 95  per  cent  of  the  Ag,  $19  per  ounce  Au,  6c.  off 
New  York  quotation  for  Cu.  This  condition  necessi- 
tated a  high  concentration,  of  30  into  I  as  a  final  ship- 
ping matte.  This  was,  of  course,  accomplished  by  re- 
concentration.  The  ores  treated  are  given  in  the  fol- 
lowing table: 

Name   of  Mine.  SiO2  Fe  CaO  Cu 

Washington    5.  42.  0.  Tr. 

Robinson   25.  15.  1.  Tr. 

Pride    64.  12.  3.  4. 

Wintergreen 4.  48.  0.  1. 

The  iron  was  all  a  sulphide,  FeS2,  except  that  from 
the  Wintergreen,  which  was  a  pyrrhotite,  Fe7S8. 

The  writer  had  been  told  by  other  metallurgists  to 
beware  of  pyrrhotite  in  a  raw  state,  but  we  experienced 
no  difficulty  with  it,  and  as  it  carried  I  per  cent  of 
copper,  we  preferred  to  use  it.  A  24-hour  run  on  ore 
used: 

Tons. 

Washington    7.60 

Robinson    81.00 

Wintergreen   36.98 

Total  ore 125.58 

Lime  rock 25.65 

Slag   55.50 


Total  charge   206.73 

Coke 16.50 

Pe.r  cent   fuel   on   ore    13.14 

Slag  assay  and  analysis  showed: 

Ag  1.1  oz. 

SiO2     41.     % 

FeO    30.8  % 

MnO    5.5% 

CaO 17.     % 

ZnO    4.     % 

98.3 
Re-smelting  matte: 

Ag 42.07  oz. 

Cu   0.2    % 

297 


PYR1TE   SMELTING. 

A  24-hour  run  on  re-concentration : 

Name  of  Mine.  Tons. 

Robinson   116.50 

Pride   28.42 

Total  ore   144.92 

Matte  .  121.52 

Lime  rock 21.90 

Tons  of  charge 288.34 

Coke 14.60 

Per  cent  fuel   on  ore    10. 

Matte: 

Ag    200.    oz. 

Au    0.5  oz. 

Cu  5.    % 

The  average  percentage  of  fuel  used  during  the  time 
the  smelter  was  in  operation  was  13.5,  being  about  I 
per  cent  less  than  the  fuel  consumption  at  Leadville. 
After  smelting  3,289  tons  of  ore  it  was  deemed  best  to 
close  the  works  and  make  a  clean-up.  The  flue-dust 
made  was  2,\  per  cent  on  the  ore  treated.  The  cost  of 
fuel  and  labor  was  $2  per  ton  of  ore.  Labor  in  this  case 
does  not  include  management,  superintendence,  etc. 

The  results,  shown  by  the  data  given  above,  will  un- 
doubtedly seem  small  in  tonnage  to  the  copper  metal- 
lurgist, but  the  ores  are  similar  to  those  handled  by  lead 
metallurgists,  and  the  tonnage  fully  equals  that  of  the 
42  by  146  in.  lead  furnace  with  a  2O-ft.  ore  column  and 
a  3-lb.  blast. 

All  of  the  above  enumerated  ores  carried  some  lead 
and  zinc,  and  notwithstanding  the  volatilization  of  the 
major  part  of  the  lead,  the  resultant  matte  carried  about 
3  per  cent  of  lead. 


298 


SMELTING  AT  MT.  LYELL,  TASMANIA  * 

Since  the  beginning  of  1902  a  smaller  number  of  fur- 
naces have  been  kept  employed  for  the  same  ore-con- 
sumption. At  the  present  there  are  five  furnaces  in  con- 
tinuous operation,  whereas  the  number  formerly  used 
to  be  seven  and  eight.  The  company  possesses  eleven 
blast  furnaces,  arranged  in  two  smelting  plants,  the 
older,  or  No.  I  plant,  containing  six  blast  furnaces,  and 
the  newer  plant,  No.  2,  five.  The  latter  were  built  ac- 
cording to  experience  gained  in  the  operation  of  the 
former,  and  were  made  considerably  larger,  the  respec- 
tive sizes,  in  the  plane  of  tuyeres,  being  as  follows :  No. 
I  plant,  40  in.  by  168  in.  (except  No.  3,  which  is  36  in. 
by  126  in.) ;  No.  2  plant,  42  in.  by  210  in. ;  the  height  in 
each  case,  from  the  tapping  to  charge  floor,  is  20  ft.  over 
all;  the  height  of  ore-column  above  tuyeres  is  9^  ft.; 
the  number  of  tuyeres  (3  in.  throughout)  is  32  in  No.  I 
plant  (24  in  No.  3  furnace),  and  40  in  No.  2  plant.  The 
furnaces  are  water-jacketed  high  up,  the  jackets  all 
being  cast  iron,  with  the  exception  of  the  small  steel- 
plate  tymp-jacket.  At  the  present  time  three  of  the 
large  furnaces  of  No.  2  plant  practically  smelt  into  first 
matte  all  the  ore  that  is  delivered,  while  two  furnaces 
of  No.  i  plant  are  devoted  to  the  concentration  of  the 
first  matte  into  converter  matte,  and  only  occasionally 
treat  ore  alone.  Under  these  circumstances,  each  fur- 
nace of  No.  2  plant  sometimes  smelts  up  to  350  tons  of 
Mt.  Lyell  pyrite  per  diem,  and  the  average  is  about  270 
tons  of  pyrite  daily.  Phenomenal  tonnages  are  occa- 
sionally reached;  thus  No.  6  furnace  recently  treated  a 

*The  Engineering  and  Mining  Journal,  May  30,  1903.  Abstracted  from  the 
report  of  the  Secretary  for  Mines,  Tasmania.  Prepared  by  the  members  of 
the  staff  of  the  Mt.  Lyell  Mining  &  Railway  Company. 

299 


PYRITE    SMELTING. 

total  of  724  tons  of  material  (matte,  silica,  limestone  and 
slag)  in  a  single  day.  This  vigorous  work  is  due  to  the 
fact  that  the  amount  of  air  formerly  distributed  to  the 
large  number  of  furnaces  is  now  supplied  to  the  smaller 
number.  Simultaneously,  the  blast  pressure  also  has 
risen,  until  it  is  now  on  a  level  with  the  pressure  made 
use  of  in  the  progressive  matte-smelting  establishments 
of  the  United  States  and  British  Columbia,  and  ranges 
from  36  to  40  oz.  at  the  blowers,  and  from  30  to  34  oz.  at 
the  furnaces,  the  difference  at  the  two  points  being  loss 
by  friction. in  hot-blast  stoves,  blast  mains  and  furnace 
connections.  To  meet  this  higher  pressure  no  altera- 
tion was  made  to  the  furnaces,  except  the  raising  of  the 
sump ;  that  is,  the  elevating  cf  the  overflow-level  of  the 
furnaces  by  several  inches  for  the  proper  trapping  of  the 
blast,  the  same  as  before. 

At  the  same  time,  important  improvements  were  also 
made  in  the  motive-power  department  by  the  installa- 
tion, in  each  smelting  plant,  of  steam-saving  appliances, 
consisting  of  Green's  economizers,  with  induced-draft 
fans  and  a  system  of  steam  superheaters.  The  economy 
effected  by  the  economizers  is  determined  as  15  per 
cent,  and  by  the  superheaters  as  16  per  cent,  total  sav- 
ing 31  per  cent.  The  waste  heat  of  the  fire-boxes  of  the 
hot-blast  stoves,  in  addition  to  that  of  the  boilers,  con- 
tributes to  this  high  result.  The  steam  plant  of  the 
smelting  works  is,  therefore,  entirely  up  to  date,  and  the 
various  improvements  have  succeeded  in  lowering  the 
cost  of  power  to  what  must  be  regarded  as  the  local 
minimum.  The  fuel  employed  is  still  chiefly  firewood, 
the  use  of  coal  being  merely  auxiliary.  The  respective 
consumptions  under  the  boilers  were,  for  the  year, 
36,443  tons  of  wood  and  1,794  tons  of  coal. 

The  work  done  in  this  department  for  the  year  was 
the  highest  yet  performed.  There  are  six  I24~h.p.  Bab- 
cock  &  Wilson  boilers  available  in  each  smelting  plant, 

300 


SMELTING  AT  MT.  LYELL,  TASMANIA. 

two  in  each  case  now  being  in  reserve.  The  average 
indicated  horse-power  was  1,905;  total  engine  revolu- 
tions, 310,000,000;  air  delivered  to  furnaces,  31,000,000,- 
ooo  cub.  ft.,  weighing  1,054,000  tons.  This  air  was 
heated  to  an  average  temperature  of  580°  F.,  thus  ab- 
sorbing 291,500,000,000  British  thermal  units  out  of  the 
combustion  of  49,000  tons  of  firewood  in  the  hot-blast 
stoves.  The  latter  have  continued  to  give  every  satis- 
faction. In  point  of  repairs,  the  eight  stoves  (four  in 
No.  i  plant,  with  56  cast-iron  U  tubes  each,  at  16  cwts., 
and  four  in  No.  2,  with  70  U  tubes  each)  have  given 
practically  no  trouble,  there,  having  been  only  about  a 
dozen  tubes  completely  replaced  since  the  beginning,  on 
account  of  burning  out.  The  number  of  hands  em- 
ployed in  the  smelter  motive-power  department  is  80, 
comprising  engine-drivers,  firemen,  cleaners,  wood- 
handlers,  etc.  It  may  be  mentioned  that,  for  the  pro- 
duction of  the  blast,  there  are  in  use  nine  vertical  com- 
pound condensing  engines,  12  in.  and  22  in.  by  18  in., 
set  up  in  marine  style,  and  direct-coupled,  by  means  of  a 
flexible  coupling,  each  to  a  No.  8  Root's  blower  of  116 
cub.  ft.  displacement;  also  one  reserve  No.  7  Root 
blower,  with  vertical  engine  attached,  ordinary  style, 
and  two  reserve  No.  7  Root  blowers,  belt  driven  from  a 
horizontal  tandem  compound  engine,  12  in.  and  20  in. 
by  30  in.  The  power  plant  thus  follows  the  unit  system  ; 
that  is,  each  furnace  has  a  blower  driven  by  an  individual 
engine,  although  the  blast  is  not  conducted  to  each  fur- 
nace separately,  but  directed  into  a  common  blast  main. 
The  condensers  are  of  the  surface  type  (1,000  sq.  ft.), 
also  with  vertical  compound  engines  6  in.  and  12  in. 
by  6  in.,  and  air-pumps  to  suit — the  latest  with  Ed- 
wardes'  pump. 

The  following  are  the  statistical  figures  of  ore  treated, 
rendered  by  the  company  for  each  quarter  of  the  year 
1901 : 

301 


Quarter    Quarter    Quarter    Quarter    Total 
ended        ended        ended         ended        for 
Sept.  30,  Dec.  31,    Mar.  31,  June  30,    year 
1901.       1901.         1902.       1902.    1901-02 
Tons.       Tons.          Tons.       Tons.      Tons. 
69  289     65  688      71  111      79  969    286  057 

(S     .... 

fluxes. 

21,257      20,731      11,680        4,841      58,509 
5,726        6,480        7,702        8,139     28,047 

PYRITE  SMELTING. 


Treated. 

Mt.  Lyell  ore 
Purchased  ores 
Metal-bearing 

Total 96,272      92,899      90,493      92,949    372,613 

It  is  thus  apparent  that  the  average  per  day  was  the 
treatment  of  over  1,000  tons  of  raw  mineral-bearing  sub- 
stances, besides  which  the  company  has  treated  in  its 
blast  furnaces  all  the  first  matte,  converter  slags  and 
linings,  flue-dust  and  similar  middle  products  formed 
in  the  process. 

The  grade  of  the  first  matte  does  not  exceed  15  per 
cent  copper,  being  a  concentration  of  from  6  to  7,  and 
more,  from  the  original  ore  into  first  matte,  all  of  which 
work  is  accomplished,  as  stated,  by  the  furnaces  of  No. 
2  plant.  The  re-treatment  and  concentration  of  this 
first  matte  by  the  furnaces  of  No.  I  plant  raises  its 
grade  to  about  50  per  cent  copper,  which  is  the  stand- 
ard required  for  proper  economical  bessemerizing  into 
blister  copper. 

The  output  of  the  furnaces  in  copper,  silver  and  gold, 
for  the  year  under  review,  is  as  follows : 


Output. 
Fine  copper 
(tons) 

in  I 

(lister 

Quarter 
ended 
Sept.  30, 
1901. 

2  630 

Quarter 
ended 
Dec.  31, 
1901. 

2579 

Quarter 
ended 
Mar.  31, 
1902. 

2520 

Quarter 
ended 
June  30, 
1902. 

1,870 

Total 
for 
year 
1901-02 

Silver,    fine 
Gold  fine   (< 

(oz 

)Z.)  . 

,)  

164',  932 
5.224 

160,102 
5.002 

182',487 
5.650 

171,133 
5.555 

678,654 

21  4n1 

The  total  money  value  of  thh  year's  output,  calcu- 
lated upon  the  changing  quotations  for  the  copper  and 
silver,  was  $3,674,803. 

The  grand  total  of  ore  treated  since  the  beginning 
of  smelting  operations  on  June  25,  1896,  up  to  March 
31, 1902,  as  given  in  the  company's  last  report,  together 
with  average  assays,  is  as  follows : 

302 


SMELTING  AT  MT.  LYELL,  TASMANIA. 

AVERAGE  ASSAY. 

Copper.  Silver.      Gold. 
Total  tons.        %  oz.  oz. 

Mt.  Lyell  Mine 1,160,684       3.00       2.81       0.101 

Purchased   ores    154,923        

Total    metal-bearing   fluxes.*.'.'.'     '  33,023        1.64       0.2J       0.020 

Grand  total  ores  and  metal-bear- 
ing fluxes 1,343,630 

It  is  interesting  to  state  that  the  average  assay  of  all 
of  the  purchased  ores,  representing  as  it  does  (with  the 
exception  of  a  quantity  of  rich  ore  shipped  to  England 
by  the  North  Mt.  Lyell  Company)  an  approximation  to 
fhe  average  value  of  the  silicious  bornite  ores  of  the  dis- 
trict, is:  Copper,  6.70  per  cent;  silver,  1.93  oz. ;  gold, 
0.002  oz.  The  Mt.  Lyell  pyrite,  therefore,  though  lower 
in  copper,  is  relatively  higher  in  silver  and  gold  than  the 
average  bornite  ore  of  the  district.  The  aggregate 
average  assay  of  all  ores  treated  by  the  company  is: 
Copper,  3.44  per  cent ;  silver,  2.70  oz.,  and  gold,  0.090 
ounces. 

The  following  were  the  last  half-yearly  average 
analyses  of  the  ores  purchased  and  smelted : 

Silica.        Iron.        Alumina. 

%  %  % 

North  Mt.  Lyell 63.70  6.22  10AO 

Lyell  Tharsis   64.00  5.08  17.25 

Mt.  Lyell  Blocks 60.91  7.91  10.60 

The  method  of  metallurgical  treatment  has  remained 
the  same  as  at  the  start,  direct  pyritic  smelting,  with 
the  use  of  only  a  very  small  percentage  of  carbonaceous 
fuel,  and  with  a  heated  blast,  and  subsequent  bessemer- 
izing  after  Manhes.  The  type  and  details  of  the  blast 
furnaces  have  required  no  alteration  from  the  original 
design.  The  use  of  a  hot  blast  for  the  furnace  treat- 
ment has  been  proved  by  experience  to  be  obligatory 
and  not  to  be  circumvented,  as  indeed  is  demonstrated 
by  a  careful  investigation  of  the  thermo-chemistry  of 
the  method.  The  process,  as  a  whole,  is  divided  into 
three  stages,  *'.  e.,  two  smeltings  into  matte,  and  the 
converting  of  the  enriched  matte  into  blister  copper. 

303 


PYRJTE    SMELTING. 

The  quantity  of  coke  used  in  the  blast-furnace  smelt- 
ing, when  calculated  on  the  ore,  is  about  5  per  cent  in 
current  work  for  the  two-fold  furnacing,-  and  6  per  cent 
on  the  ore,  including  all  incidental  coke  for  blowing-in 
purposes  and  similar  occasional  use,  while,  on  all  the 
material  fed  into  the  furnaces  (less  coke  itself),  the  per- 
centage is  only  3.25  per  cent  for  the  double  smelting. 
It  can  hardly  be  maintained  that  so  small  an  addition 
of  coke  has  any  vital  bearing  on  the  furnace  reactions, 
from  a  heat  point  of  view,  and  it  is  commonly  remarked 
that  the  coke  simply  serves  to  keep  the  tuyeres  from  be- 
coming too  hard.  It  is  fed  along  the  walls  of  the  fur- 
naces with  this  special  object  in  view.  Such  low  per- 
centages of  coke  are  possible  only  because  of  the  appli- 
cation of  the  oxygen  of  the  atmosphere  to  the  ore  mix- 
ture under  conditions  which  make  the  oxygen  perform 
a  function  somewhat  different  in  its  effect  from  that 
which  it  exercises  in  ordinary  blast-furnace  smelting, 
where  a  larger  percentage  of  carbonaceous  fuel  is  neces- 
sary. In  all  three  stages  of  the  process  the  material 
(ore  or  matte)  is  constantly  subjected  to  an  oxidizing 
action,  and  not  a  reducing  one.  The  process,  there- 
fore, in  this  respect  is  the  direct  inverse  of  ordinary 
smelting  operations  in  blast  furnaces.  A  potent  factor 
establishing  the  feasibility  of  the  furnace  smelting  is  the 
presence  of  a  heavy  percentage  of  iron  and  sulphur  in 
the  Mt.  Lyell  pyrites,  which  elements  yield  a  sufficient 
quantity  of  heat,  during  their  combustion  or  union  with 
the  oxygen  of  the  atmosphere,  to  allow  the  solid  prod- 
ucts of  combustion  to  remain  in  a  superheated  molten 
condition.  This  peculiarity  also  distinguishes  the  bes- 
semerizing  operation.  In  fact,  it  may  be  said  that  the 
Mt.  Lyell  ore-smelting  is  nothing  more  than  a  bes- 
semerizing  of  ores,  or  matte  therefrom,  direct  in  blast 
furnaces,  but  so  managed  as  to  be  continuous,  and  not 
intermittent,  as  is  the  bessemerizing  operation,  and  also 
under  perfect  control,  both  as  to  the  composition  of 

804 


SMELTING  AT  MT.  LYELL,  TASMANIA. 

slags  and  mattes,  and  the  proper  mechanical  separation 
of  these  two  products.  The  company  remains  to  this 
day  the  only  instance  of  this  idea  being  utilized,  on  a 
large  scale,  as  the  exclusive  metl.od  of  treatment.  The 
entire  length  of  time  occupied  by  the  transition  of  the 
copper  from  the  ore  into  blister  copper — that  is,  from 
the  moment  the  ore  enters  the  first  furnace  until  the 
blister  copper  issues  from  the  converters — is  only  from 
five  to  six  hours,  if  the  time  lost  through  cooling  and 
transportation  between  apparatus  is  disregarded.  An 
essential  condition  of  success  is  rapidity  of  treatment, 
for  it  is  only  by  this  means  that  the  necessary  heat  is 
concentrated  to  the  required  pitch. 

The  blast-furnace  slags  vary  between  the  following 
limits  of  composition,  the  furnace  charges  for  ore  smelt- 
ing and  matte  concentration  differing  somewhat  from 
each  other.  Limestone  is  used  only  in  the  latter  oper- 
ation, and  not  on  the  ore.  The  first  matte  is  re- 
smelted  by  itself,  as  a  rule ;  only  very  exceptionally  has 
pyritic  ore  been  used  with  it. 

Per  Per 

cent.         cent. 

Silica   36.66  to  41.70 

Iron  protoxide    50.67  to  43.14 

Calcium  oxide   1.20  to     8.16 

Barium  oxide    1  90  to     0.16 

Alumina 7.47  to     5.46 

Copper 0.25  to     0.35 

The  flue-dust  is  ground  up  and  mixed  in  a  steam- 
driven  mud-mill,  with  about  4  per  cent  of  common  clay, 
and  the  addition  of  a  little  water,  and  no  lime  is  used 
for  binding.  The  briquettes  are  of  the  size  of  ordinary 
bricks,  are  made  by  hand  in  preference  to  presses,  and 
weigh  about  14  Ib.  each.  They  are  laid  on  shelves  in  a 
large  drying  room,  and  rough-dried  by  the  heat  of  pots 
of  slag  ranged  alongside.  The  quantity  of  flue-dust  so 
handled  was  4,666  tons  for  the  year.  Its  average  assay 
was :  Copper,  3.5  per  cent ;  silver,  2.5  oz. ;  gold,  0.07  oz. 
It  contains  about  one-third  silica,  which  comes  from 

305 


PYRITE    SMELTING. 

the  dust  and  sand  accompanying  the  quartz  flux.  More 
elaborate  means  of  preparing  the  flue-dust,  like  fusion  in 
a  reverberatory  furnace,  moulding  and  burning  in  closed 
kilns,  as  well  as  a  briquetting  machine  of  good  repute, 
have  been  given  lengthy  trials,  but  have  all  been  dis- 
carded on  account  of  being  too  expensive,  and  prefer- 
ence was  finally  given  to  the  present  means,  which  is 
primitive  in  character,  but  more  satisfactory  in  regard 
to  cost  and  efficiency.  The  flue-dust  is  partly  oxidized, 
but  there  are  not  sufficient  sulphates  in  it  to  act  as 
binding  material  for  machine  briquetting,  and  the  cost 
of  the  obligatory  lime  has  decided  against  the  method. 

The  system  of  getting  rid  of  the  slag  by  granulation 
has  been  in  use  since  the  start,  but  of  late  years  it  has 
become  necessary  to  resort  to  mechanically  raising  the 
accumulating  dump  of  each  smelting  plant  to  a  higher 
level,  to  keep  the  talus  of  the  dump  within  bounds. 
This  is  effected  by  centrifugal  pumps  of  a  special  con- 
struction— the  outcome  of  the  simplification  of  preva- 
lent types  and  adaptation  to  the  special  work  to  be  per- 
formed. The  pumps  are  at  present  steam-driven,  but 
will  shortly  be  run  by  electricity.  The  slag  pumps  are 
of  small  diameter,  lo-in.  suction  by  Q-in.  discharge, 
with  i8-in.  beaters  or  vanes,  and  are  run  at  from  540  to 
600  revolutions  per  minute.  The  quantity  of  slag  ele- 
vated during  the  year  was  170,000  tons  at  No.  2  plant 
and  40,000  tons  at  No.  I  plant,  together  with  all  the 
water  entering  the  two  smelting  plants,  with  the  excep- 
tion of  that  used  for  steam  generation,  sprinkling,  etc. 
The  respective  lifts  are  15  and  n  ft.  at  present. 

The  new  sampling  works,  which  were  erected  in  place 
of  the  original  mill,  which  was  destroyed  by  fire  a 
couple  of  years  ago,  treats  the  samples  of  all  ores  and 
mineral  fluxes,  also  purchase  ores  used,  and  prepares 
them  for  the  assay  office.  The  proportions  taken  in 
transit  and  delivered  to  the  sampling  works  are :  Every 
25th  ropeway  bucket  of  open-cut  pyrites,  every  i6th 

306 


SMELTING  AT  MT.  LYELL,  TASMANIA. 

truck  of  underground  ore,  every  i8th  truck  of  mineral 
flux,  while  the  proportion  on  purchased  ores  varies  from 
all  to  J  to  Jth.  'The  balance  of  lots  goes  direct  to  the 
furnaces;  none  of  the  ores,  etc.,  are  specially  crushed, 
but  are  smelted  in  the  size  as  broken  at  the  mines. 

Converter  Plant. — The  converting  operations  are  regu- 
lated by  the  amount  of  matte  produced  in  the  blast  fur- 
naces. The  bessemerizing  plant  is  a  double  one;  that 
is,  it  consists  of  two  independent  equal-sized  depart- 
ments, each  with  facilities  for  turning  out  from  25  to  40 
tons  of  copper  a  day.  The  total  number  of  vessels  is 
14  (12  in  use),  vessel  stands,  6;  and  there  are  two  re- 
melting  furnaces  with  a  No.  5  rotary  blower  each,  with 
vertical  engine  attached;  two  high-class  Fraser  & 
Chalmers  horizontal  compound  condensing  blowing 
engines,  16  and  24  by  30  in.,  with  air-cylinders  30  in. 
by  30  in.,  delivering  3,000  cub.  ft.  of  free  air  at  60  revo- 
lutions ;  a  14  by  3^  by  10  in.  duplex  Worthington  high- 
pressure  pump;  an  accumulator;  and  all  other  neces- 
sary paraphernalia  for  the  handling  and  tilting  of  the 
vessels,  including  hydraulic  cars  for  shifting  same,  trav- 
eling crane,  etc.,  together  with  the  necessary  machinery, 
grinding  pans,  etc.,  for  the  preparation  of  the  vessel  lin- 
ings ;  also  drilling  machines  for  drilling  the  blister  cop- 
per for  sample.  Steam  is  supplied  by  four  7o-h.p.  multi- 
tubular  boilers.  In  the  motive-power  department  the 
average  indicated  horse-power  developed  for  the  year 
was  300,  and  the  amount  of  wood  fuel  consumed  13,043 
tons.  The  average  blast-pressure  is  8  Ib.  per  sq.  in. 
at  the  vessels. 

The  clay  for  the  vessel  linings  is  a  fine  white  variety 
of  refractory  nature,  won  in  the  immediate  vicinity  of 
the  converter  plant,  and  the  silica  is  supplied  by  the 
screened  fine  or  refuse  from  the  quartz-crushing  plant 
at  the  quarries.  In  these  important  respects  the  com- 
pany is  therefore  fortunately  situated.  The  composition 
of  the  clay  is  as  follows : 

307 


PYRITE    SMELTING. 

Per  cent. 

Silica   «2.52 

Alumina   23.89 

Iron    oxide    0-26 

.  Calcium   oxide    0  25 

Magnesium  oxide    0. 40 

Water  and  undetermined   12.68 

100.00 

The  number  of  'blows'  which  a  lining  will  stand,  until 
corroded  so  thin  that  the  vessel  has  to  be  removed,  is 
from  five  to  seven. 

This  portion  of  the  reduction  works  is  also  unique,  for 
it  is  the  only  case  of  bessemer  works  for  copper  in  Aus- 
tralia. The  first  converter  was  started  on  January  14, 
1897.  The  style  of  vessel  is  that  known  as  the  Stalmann 
type,  which  has  proved  satisfactory ;  it  is  slight  in  re- 
pairs, a  fact  due  largely  to  the  square  shape  of  the  ves- 
sels. The  tilting-gear  is  simple  and  effective,  the  rack 
being  on  the  cylinder  itself,  which  travels  horizontally 
on  the  hollowed  piston-rod,  through  which  the  pressure 
water  enters  and  leaves. 

The  production  of  the  bessemerizing  plant  for  the  four 
quarters  of  the  year  is  given  above,  under  the  output  of 
the  furnaces  in  metals.  Since  the  beginning  of  opera- 
tions to  the  end  of  the  company's  last  half  year  (March 
31)  the  total  results  are  as  follows:  Blister  copper, 
40,168  tons,  of  an  average  assay  per  ton  of:  Copper, 
98.83  per  cent;  silver,  81.36  oz. ;  gold,  3.124  oz.  The 
total  content  was :  Copper,  39,698  tons ;  silver,  3,268,016 
oz. ;  gold,  125,498  ounces. 

Adding  on  the  production  for  the  last  quarter,  the 
figures  become  the  following,  from  the  commencement 
of  work  to  July  I,  1902  :  Blister  copper,  42,060  tons,  con- 
taining: Copper,  41,568  tons;  silver,  3,439^49  oz. ; 
gold,  131,053  ounces. 

The  quantity  of  converter  matte  treated  by  the  con- 
verters from  the  beginning  to  March  31,  is  87,229  tons, 
of  an  average  assay  of :  Copper,  49.48  per  cent ;  silver, 
39.34  oz. ;  and  gold  1.480  ounces. 


SMELTING  AT  MT.  LYELL,  TASMANIA. 

The  blister  copper  is  now  poured  into  plates,  or 
cakes,  measuring  16  in.  by  24  in.  and  2,\  in.  thick,  the 
former  bars  or  pigs  having  been  abandoned.  Five  hun- 
dred plates  constitute  a  lot  or  parcel  of  50  tons,  the 
sample  of  which  is  kept  distinct.  Sampling  is  done  by 
drilling  two  -J-in.  holes  through  each  plate,  with  power- 
driven  drill  presses.  The  blister  copper  is  all  shipped 
to  the  United  States,  via  London,  and  is  refined  by  the 
Baltimore  Copper  Smelting  and  Rolling  Company  in 
Maryland,  on  a  toll  arrangement,  the  products  being 
turned  over  to  the  company.  The  products,  i.  e.,  elec- 
trolytic copper,  as  ingots,  wire-bars,  etc.,  on  the  one 
hand,  and  fine  silver  and  fine  gold  on  the  other,  are  sold 
by  the  company,  the  two  precious  metals  being  disposed 
of  at  the  United  States  Mints,  and  the  copper  in  the 
open  market.  It  is  chiefly  exported  to  Europe,  its  iden- 
tity being  merged  in  that  of  the  well-known  brand 
"B.E.R." 

A  note  from  Mr.  Alfred  Miller,  appended  to  the 
article  above  abstracted,  gives  some  additional  informa- 
tion. It  says  that,  since  the  article  was  written,  impor- 
tant changes  have  been  effected  in  the  smelting  method 
by  bringing  it  up  to  what  may  be  called  "ideal  pyntic 
smelting.''  Ore  smelting  in  No.  2  plant  has  been  con- 
tinued since  the  middle  of  November  last,  without  the 
use  of  coke  (but  with  heated  blast,  although  of  a  lower 
temperature  than  that  formerly  used),  and  at  No.  I 
plant  both  ore  and  matte  have  been  smelted  without 
the  use  of  the  hot  blast  (but  with  the  former  addition  of 
a  small  percentage  of  coke).  These  innovations  have 
been  attended  with  no  trouble  whatsoever,  and  may  now 
be  considered  permanently  established,  the  results  being 
favorable,  and  tending  toward  an  increase  of  furnace 
capacity.  Needless  to  say,  they  effect  a  considerable 
annual  saving,  and  it  is  expected  that  still  further  im- 
provements and  economies  will  be  achievable  in  the 
course  of  time.  Four  furnaces  are  now  doing  the  work 

309 


PYRITE  SMELTING. 

referred  to  in  the  article  as  being  done  by  five,  three  of 
the  four  being  constantly  on  ore,  and  the  fourth  con- 
centrating the  first  matte  into  converter  matte. 

The  treatment  costs  for  the  company's  half  year, 
ended  September  30,  1902,  were  as  follows  (reduced  to 
United  States  currency):  Mining,  $0.5002;  removal  of 
overburden,  $0.50;  smelting,  $3.3648;  converting, 
$0.3612 ;  total,  $4.7262. 

During  the  half  year  mentioned  there  were  treated 
159,450  tons  of  Mount  Lyell  ore,  of  an  average  value  of: 
Copper,  2.36  per  cent;  silver,  2.23  oz.,  and  gold,  0.069 
oz. ;  together  with  18,537  tons  of  metal-bearing  fluxes, 
of  an  average  assay  value  of:  Copper,  1.70  per  cent; 
silver,  0.24  oz. ;  and  gold,  0.026  oz. ;  and  5,689  tons  of 
purchased  ores,  making  the  grand  total  for  the  half 
year,  183,676  tons,  and  raising  the  grand  total  since  the 
beginning  to  1,532,306  tons  of  ore. 


310 


ORE    DRESSING 

By  ROBERT  H.  RICHARDS 

This  magnificent  contribution  to  metallurgical  literature  ia 
now  ready,  after  many  years  of  careful  preparation  by  the  author, 
who  is  one  of  the  ablest  experts  on  the  question.  In  this  ex- 
cellent treatise  the  ore  dressing  theory  is  thoroughly  developed, 
and  an  inexhaustible  mine  of  useful  facts  and  practical  experi- 
ments is  brought  forth  that  virtually  outrivals  any  other  work 
ever  before  issued  on  any  branch  of  mechanical  and  metallurgical 
engineering.  The  unswerving  aim  of  the  author  has  been  to  elu- 
cidate to  the  working  student  modern  American  practice,  referring 
for  comparison  to  European,  and  to  so  expound  the  principles 
of  the  art  as  at  present  understood  as  to  make  advance  easy  in 
the  future.  The  plan  of  the  book  is  essentially  practical,  and,  is 
divided  into  four  main  parts,  viz.:  Crushing,  Separating,  Con- 
centrating and  Washing,  Accessory  Apparatus  and  Mill  Process, 
and  Management.  The  ifumerous  subdivisions  include  elaborate 
chapters  on  Gravity  Stamps,  Screen  Sizing  and  its  Principles, 
Classifiers,  Hand  Picking,  Jigs  and  Laws  of  Jigging,  Slime  Con- 
centration and  Amalgamation. 

This  superb  work  is  beyond  all  doubt  or  question  a  veritable 
masterpiece  of  technical  literature,  and  should  occupy  a  promi- 
nent place  in  every  industrial  library.  Mining,  metallurgical  and 
mechanical  engineers  cannot  afford  to  be  without  it,  as  it  is 
specifically  the  kind  of  literature  the  profession  nowadays  demand 
as  an  infallible  guide  to  practical  work. 

Chapter  I.— General  Principles.  Chapter  XIII.— Hand  Picking. 

Part  I.— Breaking,    Crushing    and  Chapter  XIV.— Jigs. 

ChaP^ermfL-Prne!^inary  Crushing.  Chapter  XV.-Laws  of  Jigging. 

Chapter  III.— Rolls.  Chapter  XVI.— Fine  Sand  and  Slime 
Chapter  IV. — Steam,  Pneumatic  and  Concentrators. 

Spring  Stamps.  Chapter  XVII. — Amalgamation. 

Chapter  V. — Gravity  Stamps.  _,  -VTTTTT      *r-      u  -n 

ChXter  Vl.-Pulverizers  other  than  ^P**  XVin.-Mlscellaneous  Pro- 

Gravity  Stamps.  cess  of  Separation. 

Chapter  VII. — Laws  of  Crushing.  Part  III. — Accessory  Apparatus : 

Part  II. — Separating,  Concentrating  Chapter  XIX. — Accessory  Apparatus. 

or  Washing:  Part    IV.— Mill  Processes  and  Man- 

Chapter  VIII. — Preliminary  Washers.  agement : 

Chapter  IX. — Sizing  Screens.  Chapter  XX. —  Summarv    of  Princi- 
Chapter     X. —  Principles    of    Screen  pies  and  Outlines  of  Mills. 

Sizing.  Chapter  XXI.  —  General     Ideas     on 
Chapter  XI. — Classifiers.  Milling. 

Chapter  XII. — Laws  of  Classifying  by  Appendix,  Tables  and  Other    Useful 

Free  Settling  in  Watsr.  Information.     Index. 

Two  Volumes.    Octavo,  Cloth.     1250  Pages,  profusely  illustrated. 

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THE 
NATURE  OF  ORE  DEPOSITS 


BY 

DR.  RICHARD  BECK 

Professor  of  Geology  and  Economic  Geology, 
Freiberg  Mining  Academy 

TKANSLATEI)  AND  EEVISED  BY 

WALTER  HARVEY  WEED 

U.  8.   Geological  Survey 

« 

An  intelligent  dissertation  on  Ore  Deposition,  writ- 
ten by  an  eminent  expert  on  the  subject  and  translated 
and  thoroughly  revised  to  date  by  Walter  Harvey  Weed, 
of  the  U.  S.  Geological  Survey,  from  the  original 
German  of  Dr.  Richard  Beck.  Treating  in  an  author- 
itative style  the  nature  and  methods  of  occurrence  of  ore 
deposits  in  all  parts  of  the  world,  together  with  detailed 
descriptions  and  characteristic  cross-sections  of  veins, 
ore  bodies  and  ores  from  many  famous  mines  of  ancient 
and  modern  times.  The  data  embodied  in  this  important 
manual  distinctly  applies  to  local  conditions,  and  the 
almost  inexhaustible  amount  of  general  and  precise 
information  scattered  through  its  various  pages  essen- 
tially makes  the  work  a  splendid  text-book  for  college 
classes  in  the  study  of  economic  geology. 

Two  volumes,  octavo,  cloth  binding,  profusely  illustrated, 
including  272  figures  and  map.        Price,  $8.00,  postpaid. 

The  Engineering  and  Mining  Journal 

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The  Chemistry  of  Cyanide 
Solutions  Resulting  from  the 
Treatment  of  Ores 


By  J.  C.  CLENNELL 

The  author's  distinct  object  in  this  treatise  has 
been  to  avoid  in  a  measure  the  recording-  of  the  results 
of  any  special  researches  on  individual  obscure  points, 
and  to  present  a  comprehensive  and,  as  far  as  possible, 
a  complete  review  of  the  entire  subject.  Compact  and 
reliable  data  applying-  to  the  chemistry  of  cyaniding  has 
been  in  the  recent  past  ignored  or  slightly  referred  to 
by  the  numerous  authorities  on  the  question,  and  the 
author  has  endeavored  to  clearly  present  the  various 
exemplifications  of  existing  methods  with  a  minute 
completeness  which  will  instantly  recommend  the  volume 
to  all  practical  workers  in  the  industry. 

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THE  COPPER  MINES  OF 
LAKE  SUPERIOR 


By  T.  A.  RICKARD 


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clear,  bold  type,  handsomely  illustrated  and  written  in 
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during  the  latter  part  of  1904.  It  is  needless  to  remark 
that  the  famous  and  historic  copper  mines  of  Lake 
Superior  are  not  only  important  from  an  industrial 
base,  but  in  their  history  and  development  they  embody 
many  features  which  are  essentially  salient  to  mining 
men,  mine  investors,  and  all  others  connected  with  the 
mineral  resources  of  the  country.  The  author  has 
vigorously  handled  his  theme,  and  the  valuable  data 
incorporated  in  this  treatise  is  calculated  to  attract  not 
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GEOLOGY  APPLIED  TO 
MINING 


BY 

JOSIAH  EDWARD  SPURR,  A.M. 


The  aim  of  the  author  in  this  most  excellent  dis- 
sertation on  the  physical  history  of  the  earth  is  to 
intelligently  impart  to  the  reader  a  comprehensive  study 
of  the  salient  geological  principles,  a  knowledge  of 
which  is  imperatively  essential  to  the  understanding 
and  proper  exploitation  of  ore  deposits.  This  useful 
manual,  which  has  just  been  issued  by  the  publishers 
after  many  months  of  careful  preparation,  is  destined  to 
prove  of  the  greatest  practical  value  and  aid  to  the 
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study  of  economic  geology. 


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The  Elements  of 
Mining  and  Quarrying 

BY 

SIR  CLEMENT  LE  NEVE  FOSTER 

The  latest  and  most  reliable  treatise  on  the  art  of  extracting 
useful  minerals  from  the  earth's  crust.  This  admirable  book  has 
been  written  by  Sir  Clement  Le  Neve  Foster,  who  was  the 
greatest  authority  on  the  subject,  and  the  data  embodied  in  it 
will  strongly  appeal  to  the  elementary  student  and  beginner,  as 
the  work  elucidates  the  principles  of  mining  and  quarrying  in 
an  exceedingly  simple  and  straightforward  style,  besides  contain- 
ing numerous  hints  and  suggestions  which  will  help  the  seeker 
after  knowledge  to  create  a  system  of  his  own  for  arranging  his 
ideas  methodically.  In  conclusion,  the  publishers  would  state 
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figure,  has  been  a  keenly  felt  want  for  many  years,  and  the  pres- 
ent excellent  volume  thoroughly  fills  that  particular  need. 

GENERAL  CONTENTS. 

Chapter  I. — Occurrence.  Chapter  IX. — Drainage. 

Chapter  II. — Discovery.  Chapter  X. — Ventilation. 

Chapter  III. — Boring.  Chapter  XI. — Lighting. 

Chapter  IV. — Excavations — Ex-  Chapter  XII. — Access. 

plosives.  Chapter  XIII. — Dressing. 

Chapter  V. — Support — Timber-  Chapter  XIV. — Legislation. 

ing.  Chapter  XV. — Condition  of  the 

Chapter  VI. — Exploitation.  workmen. 

Chapter  VII. — Haulage.  Chapter  XVI. — Accidents. 
Chapter  VIII. — Hoisting  or 

Winding. 

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THE 

SAMPLING  and  ESTIMATION 
OF  ORE  IN  A  MINE 

By  T;  A.  RICKARD 

Editor  of  The  Engineering:  and  Mining  Journal 

This  most  excellent  book  is  a  reprint  with  revision  and 
amplification  of  the  numerous  articles  which  have  recently 
appeared  in  the  columns  of  "The  Engineering  and  Mining 
Journal/'  Sampling  and  mine  valuation  are  eminently 
practical  subjects,  and  in  this  work  they  are  handled  in 
detail  by  engineers  and  experts  of  the  first  rank  who  have 
had  world-wide  experience  in  these  matters.  Mr.  Rickard's 
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information  hitherto  unpublished.  Their  importance  has 
been  much  increased  by  the  subsequent  discussion,  also  ap- 
pearing in  the  present  volume.  To  students,  mine  direc- 
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ACROSS  THE 
SAN  JUAN  MOUNTAINS 

BY 

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EDITOR  OF 

The  Engineering  and  Mining  Journal 

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